Contingent cardio-protection for epilepsy patients

ABSTRACT

Disclosed are methods and systems for treating epilepsy by stimulating a main trunk of a vagus nerve, or a left vagus nerve, when the patient has had no seizure or a seizure that is not characterized by cardiac changes such as an increase in heart rate, and stimulating a cardiac branch of a vagus nerve, or a right vagus nerve, when the patient has had a seizure characterized by cardiac changes such as a heart rate increase.

CROSS-REFERENCE TO RELATED APPLICATIONS

This presently being filed application is a continuation-in-part of andclaims priority to co-pending U.S. patent application Ser. No.16/188,356 entitled “Detecting or Validating a Detection of a StateChange from a Template of Heart Rate Derivative Shape or Heart Beat WaveComplex”, filed on Nov. 13, 2018, which is a continuation of and claimspriority to U.S. patent application Ser. No. 15/246,313 entitled“Detecting or Validating a Detection of a State Change from a Templateof Heart Rate Derivative Shape or Heart Beat Wave Complex”, filed onAug. 24, 2016 (Now U.S. Pat. No. 10,130,294) which is a continuation ofand claims priority to U.S. patent application Ser. No. 14/583,099entitled “Detecting or Validating a Detection of a State Change from aTemplate of Heart Rate Derivative Shape or Heart Beat Wave Complex”,filed on Dec. 25, 2014 (Now U.S. Pat. No. 9,451,894) which is acontinuation of and claims priority to U.S. patent application Ser. No.13/899,267 entitled “Detecting or Validating a Detection of a StateChange from a Template of Heart Rate Derivative Shape or Heart Beat WaveComplex”, filed on May 21, 2013 (Now U.S. Pat. No. 8,948,855) which is acontinuation of and claims priority to U.S. patent application Ser. No.12/886,419 entitled “Detecting or Validating a Detection of a StateChange from a Template of Heart Rate Derivative Shape or Heart Beat WaveComplex”, filed on Sep. 20, 2010 (Now U.S. Pat. No. 8,452,387) which isa continuation-in-part of and claims priority to U.S. patent applicationSer. No. 12/884,051 entitled “Detecting or Validating a Detection of aState Change from a Template of Heart Rate Derivative Shape or HeartBeat Wave Complex”, filed on Sep. 16, 2010 (Now U.S. Pat. No. 8,571,643)and this presently being filed application is a continuation-in-part ofand claims priority to co-pending U.S. patent application Ser. No.16/679,216, entitled “Contingent Cardio-Protection For EpilepsyPatients”, filed on Nov. 10, 2019 which is a continuation-in-part of andclaims priority to co-pending U.S. patent application Ser. No.15/437,155 entitled “Contingent Cardio-Protection For EpilepsyPatients”, filed on Feb. 20, 2017, which claims priority to and is adivisional application of U.S. patent application Ser. No. 14/050,173entitled “Contingent Cardio-Protection For Epilepsy Patients”, filed onOct. 9, 2013 (now U.S. Pat. No. 9,579,506), which claims priority to andis a continuation-in-part of U.S. patent application Ser. No. 13/601,099entitled “Contingent Cardio-Protection For Epilepsy Patients”, filed onAug. 31, 2012 (now U.S. Pat. No. 9,314,633), which claims priority toand is a continuation-in-part of U.S. patent application Ser. No.12/020,195 entitled “Method, Apparatus and System for Bipolar ChargeUtilization during Stimulation by an Implantable Medical Device”, filedon Jan. 25, 2008 (now U.S. Pat. No. 8,260,426) and claims priority toand is a continuation-in-part of U.S. patent application Ser. No.12/020,097 entitled “Changeable Electrode Polarity Stimulation by anImplantable Medical Device”, filed on Jan. 25, 2008 (now U.S. Pat. No.8,565,867) all of which are incorporated herein by reference in theirentireties.

BACKGROUND OF THE DISCLOSURE

This disclosure relates generally to medical devices, and, moreparticularly, to methods, apparatus, and systems for performing vagusnerve stimulation (VNS) for treating epileptic seizures characterized bycardiac changes, including ictal tachycardia.

DESCRIPTION OF THE RELATED ART

While seizures are the best known and most studied manifestation ofepilepsy, cardiac alterations are prevalent and may account for the highrate of sudden unexpected death (SUDEP) in these patients. Thesealterations may include changes in rate (most commonly tachycardia,rarely bradycardia or asystole), rhythm (PACs, PVCs,), conduction (e.g.,bundle branch block) and repolarization abnormalities (e.g., Q-Tprolongation, which occurs primarily during (ictal) but also betweenseizures (inter-ictally). In addition, S-T segment depression (a sign ofmyocardial ischemia) is observed during epileptic seizures. Significantelevations in heart-type fatty acid binding protein (H-FABP), acytoplasmic low-molecular weight protein released into the circulationduring myocardial injury have been documented in patients with epilepsyand without evidence of coronary artery disease, not only duringseizures but also during free-seizure periods. H-FABP is a moresensitive and specific marker of myocardial ischemia than troponin I orCK-MB. Elevations in H-FABP appear to be un-correlated with duration ofillness, of the recorded seizures, or with the Chalfont severity scoreof the patients.

The cardiac alterations in epilepsy patients, both during and betweenseizures, have a multi-factorial etiology, but a vago-sympatheticimbalance seems to play a prominent role in their generation. Themajority of epileptic seizures enhance the sympathetic tone (plasmanoradrenaline and adrenaline rise markedly after seizure onset) causingtachycardia, arterial hypertension and increases in the respiratoryrate, among others. Recurrent and frequent exposure to the outpouring ofcatecholamines associated with seizures in patients withpharmaco-resistant epilepsies may, for example, account forabnormalities that increase the risk of sudden death such asprolongation of the Q-T interval which leads to often fataltachyarrhythmias such as torsade de pointe. Further evidence in supportof the role of catecholamines in SUDEP is found in autopsies of SUDEPvictims, revealing interstitial myocardial fibrosis (a risk factor forlethal arrhythmias), myocyte vacuolization, atrophy of cardiomyocytes,leukocytic infiltration, and perivascular fibrosis. Restoration of thesympathetic-parasympathetic tone to normal levels, a therapeuticobjective that may be accomplished by enhancing parasympathetic activitythrough among others, electrical stimulation of the vagus nerve, maydecrease the rate and severity of cardiac and autonomic co-morbiditiesin these patients.

While there have been significant advances over the last several decadesin treatments for epileptic seizures, the management ofco-morbidities—in particular the cardiac alterations associated withseizures—remains largely unaddressed. There is a need for improvedepilepsy treatments that address cardiac impairments associated withseizures. Pharmacological therapies for neurological diseases (includingepilepsy) have been available for many decades. A more recent treatmentfor neurological disorders involves electrical stimulation of a targettissue to reduce symptoms or effects of the disorder. Such therapeuticelectrical signals have been successfully applied to brain, spinal cord,and cranial nerves tissues improve or ameliorate a variety ofconditions. A particular example of such a therapy involves applying anelectrical signal to the vagus nerve to reduce or eliminate epilepticseizures, as described in U.S. Pat. Nos. 4,702,254, 4,867,164, and5,025,807, which are hereby incorporated herein by reference in theirentirety.

The endogenous electrical activity (i.e., activity attributable to thenatural functioning of the patient's own body) of a neural structure maybe modulated in a variety of ways. One such way is by applying exogenous(i.e., from a source other than the patient's own body) electrical,chemical, or mechanical signals to the neural structure. In someembodiments, the exogenous signal (“neurostimulation” or“neuromodulation”) may involve the induction of afferent actionpotentials, efferent action potentials, or both, in the neuralstructure. In some embodiments, the exogenous (therapeutic) signal mayblock or interrupt the transmission of endogenous (natural) electricalactivity in the target neural structure. Electrical signal therapy maybe provided by implanting an electrical device underneath the skin of apatient and delivering an electrical signal to a nerve such as a cranialnerve.

In one embodiment, the electrical signal therapy may involve detecting asymptom or event associated with the patient's medical condition, andthe electrical signal may be delivered in response to the detection.This type of stimulation is generally referred to as “closed-loop,”“active,” “feedback,” “contingent” or “triggered” stimulation.Alternatively, the system may operate according to a predeterminedprogram to periodically apply a series of electrical pulses to the nerveintermittently throughout the day, or over another predetermined timeinterval. This type of stimulation is generally referred to as“open-loop,” “passive,” “non-feedback,” “non-contingent” or“prophylactic,” stimulation.

In other embodiments, both open- and closed-loop stimulation modes maybe used. For example, an open-loop electrical signal may operate as a“default” program that is repeated according to a programmed on-time andoff-time until a condition is detected by one or more body sensorsand/or algorithms. The open-loop electrical signal may then beinterrupted in response to the detection, and the closed-loop electricalsignal may be applied—either for a predetermined time or until thedetected condition has been effectively treated. The closed-loop signalmay then be interrupted, and the open-loop program may be resumed.Therapeutic electrical stimulation may be applied by an implantablemedical device (IMD) within the patient's body or, in some embodiments,externally.

Closed-loop stimulation of the vagus nerve has been proposed to treatepileptic seizures. Many patients with intractable, refractory seizuresexperience changes in heart rate and/or other autonomic body signalsnear the clinical onset of seizures. In some instances the changes mayoccur prior to the clinical onset, and in other cases the changes mayoccur at or after the clinical onset. Where the changes involves heartrate, most often the rate increases, although in some instances a dropor a biphasic change (up-then-down or down-then-up) may occur. It ispossible using a heart rate sensor to detect such changes and toinitiate therapeutic electrical stimulation (e.g., VNS) based on thedetected change. The closed-loop therapy may be a modified version of anopen-loop therapy. See, e.g., U.S. Pat. Nos. 5,928,272, and 6,341,236,each hereby incorporated by reference herein. The detected change mayalso be used to warn a patient or third party of an impending oroccurring seizure.

VNS therapy for epilepsy patients typically involves a train ofelectrical pulses applied to the nerve with an electrode pair includinga cathode and an anode located on a left or right main vagal trunk inthe neck (cervical) area. Only the cathode is capable of generatingaction potentials in nerve fibers within the vagus nerve; the anode mayblock some or all of the action potentials that reach it (whetherendogenous or exogenously generated by the cathode). VNS as an epilepsytherapy involves modulation of one or more brain structures. Therefore,to prevent the anode from blocking action potentials generated by thecathode from reaching the brain, the cathode is usually located proximalto the brain relative to the anode. For vagal stimulation in the neckarea, the cathode is thus usually the upper electrode and the anode isthe lower electrode. This arrangement is believed to result in partialblockage of action potentials distal to or below the anode (i.e., thosethat would travel through the vagus nerve branches innervating thelungs, heart and other viscerae). Using an upper-cathode/lower-anodearrangement has also been favored to minimize any effect of the vagusnerve stimulation on the heart.

Stimulation of the left vagus nerve, for treatment of epilepsy hascomplex effects on heart rate (see Frei & Osorio, Epilepsia 2001), oneof which includes slowing of the heart rate, while stimulation of theright vagus nerve has a more prominent bradycardic effect. Electricalstimulation of the right vagus nerve has been proposed for use in theoperating room to slow the heart during heart bypass surgery, to providea surgeon with a longer time period to place sutures between heartbeats(see, e.g., U.S. Pat. No. 5,651,373). Some patents discussing VNStherapy for epilepsy treatment express concern with the risk ofinadvertently slowing the heart during stimulation. In U.S. Pat. No.4,702,254, it is suggested that by locating the VNS stimulationelectrodes below the inferior cardiac nerve, “minimal slowing of theheart rate is achieved” (col. 7 lines 3-5), and in U.S. Pat. No.6,920,357, the use of a pacemaker to avoid inadvertent slowing of theheart is disclosed.

Cranial nerve stimulation has also been suggested for disorders outsidethe brain such as those affecting the gastrointestinal system, thepancreas (e.g., diabetes, which often features impaired production ofinsulin by the islets of Langerhans in the pancreas), or the kidneys.Electrical signal stimulation of either the brain alone or the organalone may have some efficacy in treating such medical conditions, butmay lack maximal efficacy.

While electrical stimulation has been used for many years to treat anumber of conditions, a need exists for improved VNS methods of treatingepilepsy and its cardiac co-morbidities as well as other brain andnon-brain disorders.

This disclosure relates to medical device systems and methods capable ofdetecting or validating a detection and, in some embodiments, treatingan occurring or impending state change.

Approximately 60 million people worldwide are affected with epilepsy, ofwhom roughly 23 million suffer from epilepsy resistant to multiplemedications. In the USA alone, the annual cost of epilepsy care is USD12 billion (in 1995 dollars), most of which is attributable to subjectswith pharmaco-resistant state changes. Pharmaco-resistant state changesare associated with an increase mortality and morbidity (compared to thegeneral population and to epileptics whose state changes are controlledby medications) and with markedly degraded quality of life for patients.State changes may impair motor control, responsiveness to a wide classof stimuli, and other cognitive functions. The sudden onset of apatient's impairment of motor control, responsiveness, and othercognitive functions precludes the performance of necessary and evensimple daily life tasks such as driving a vehicle, cooking, or operatingmachinery, as well as more complex tasks such as acquiring knowledge andsocializing.

Therapies using electrical currents or fields to provide a therapy to apatient (electrotherapy) are beneficial for certain neurologicaldisorders, such as epilepsy. Implantable medical devices have beeneffectively used to deliver therapeutic electrical stimulation tovarious portions of the human body (e.g., the vagus nerve) for treatingepilepsy. As used herein, “stimulation,” “neurostimulation,”“stimulation signal,” “therapeutic signal,” or “neurostimulation signal”refers to the direct or indirect application of an electrical,mechanical, magnetic, electro-magnetic, photonic, acoustic, cognitive,and/or chemical signal to an organ or a neural structure in thepatient's body. The signal is an exogenous signal that is distinct fromthe endogenous electro-chemical activity inherent to the patient's bodyand also from that found in the environment. In other words, thestimulation signal (whether electrical, mechanical, magnetic,electro-magnetic, photonic, acoustic, cognitive, and/or chemical innature) applied to a cranial nerve or to other nervous tissue structurein the present disclosure is a signal applied from a medical device,e.g., a neurostimulator.

A “therapeutic signal” refers to a stimulation signal delivered to apatient's body with the intent of treating a medical condition through asuppressing (blocking) or modulating effect to neural tissue. The effectof a stimulation signal on neuronal activity may be suppressing ormodulating; however, for simplicity, the terms “stimulating”,suppressing, and modulating, and variants thereof, are sometimes usedinterchangeably herein. In general, however, the delivery of anexogenous signal itself refers to “stimulation” of an organ or a neuralstructure, while the effects of that signal, if any, on the electricalactivity of the neural structure are properly referred to as suppressionor modulation.

Depending upon myriad factors such as the history (recent and distant)of the nervous system, stimulation parameters and time of day, to name afew, the effects of stimulation upon the neural tissue may be excitatoryor inhibitory, facilitatory or disfacilitatory and may suppress,enhance, or leave unaltered neuronal activity. For example, thesuppressing effect of a stimulation signal on neural tissue wouldmanifest as the blockage of abnormal activity (e.g., epileptic statechanges) see Osorio et al., Ann Neurol 2005; Osorio & Frei IJNS 2009).The mechanisms thorough which this suppressing effect takes place aredescribed in the foregeoing articles. Suppression of abnormal neuralactivity is generally a threshold or suprathreshold process and thetemporal scale over which it occurs is usually in the order of tens orhundreds of milliseconds. Modulation of abnormal or undesirable neuralactivity is typically a “sub-threshold” process in the spatio-temporaldomain that may summate and result under certain conditions, inthreshold or suprathreshold neural events. The temporal scale ofmodulation is usually longer than that of suppression, encompassingseconds to hours, even months. In addition to inhibition ordysfacilitation, modification of neural activity (wave annihilation) maybe exerted through collision with identical, similar or dissimilarwaves, a concept borrowed from wave mechanics, or through phaseresetting (Winfree).

In some cases, electrotherapy may be provided by implanting anelectrical device, i.e., an implantable medical device (IMD), inside apatient's body for stimulation of a nervous tissue, such as a cranialnerve. Generally, electrotherapy signals that suppress or modulateneural activity are delivered by the IMD via one or more leads. Whenapplicable, the leads generally terminate at their distal ends in one ormore electrodes, and the electrodes, in turn, are coupled to a targettissue in the patient's body. For example, a number of electrodes may beattached to various points of a nerve or other tissue inside a humanbody for delivery of a neurostimulation signal.

Although non-contingent, programmed periodic stimulation (also referredto as “open-loop,” “passive,” or “non-feedback” stimulation (i.e.,electrotherapy applied without reference to sensed information)) is theprevailing modality, contingent (also referred to as “closed-loop,”“active,” or “feedback” stimulation (i.e., electrotherapy applied inresponse to sensed information)) stimulation schemes have been proposed.Included in such proposed stimulation schemes are electrotherapy appliedin response to an indication of an impending, occurring, or occurredstate change, with the intent of reducing the duration, the severity, orboth of a state change or a post-state change recovery period. However,such stimulation schemes would require reasonably sensitive techniquesfor indicating an impending, occurring, or occurred state change.

Even if closed-loop neurostimulation, or any other therapy for epilepsy,is not performed, reasonably sensitive and/or specific techniques forindicating an impending, occurring, or occurred state change would bedesirable for warning of state changes to minimize risk of injuries andfor logging to assess the state of the disease and assess the efficacyof therapies. Numerous studies have shown that self-reporting bypatients, such as in state change diaries, generally only captures abouthalf of all state changes having both electroencephalographic (EEG) andclinical signatures. Roughly a third of all patients do not identify anyof their state changes. Detection of brain state changes may beaccomplished using different body signals, but cortical electricalsignals are most commonly used for this purpose. For multiple reasons(e.g., signal to noise ratio, stability of signals, etc.) intracranialand not scalp recordings are the modality of choice for prolonged (e.g.,weeks to years) recording of cortical signals. However, since use ofintracranial signals requires costly and burdensome surgical proceduresthat are associated with certain potentially serious complications, theyare neither accessible nor acceptable to the majority of hundreds ofthousands of patients that could benefit from them. Use of non-cerebralor extra-cerebral signals has emerged as a viable, useful, and highlycost-effective alternative to electrical cortical signals for thedetection, warning, and logging of brain state changes, such asepileptic seizures.

In one aspect of the present disclosure, a method for indicating anoccurrence of a state change is provided. In one aspect of the presentdisclosure, the method comprises obtaining a time series of cardiac datafrom a patient; determining a reference heart rate parameter from saidcardiac data; determining a heart rate derivative shape from said timeseries of cardiac data, wherein said heart rate derivative shapecomprises at least one characteristic selected from a number of phasesrelative to said reference heart rate parameter, a number of extrema ofsaid heart rate derivative, a number of directions of change of saidheart rate derivative, an area under the curve of at least one phase, anumber of positive phases, or a number of negative phases; andindicating an occurrence of a state change based upon a determinationthat said heart rate derivative shape matches a state change template insaid at least one characteristic, wherein said at least onecharacteristic of said state change template comprises two or morephases relative to said reference heart rate parameter, two or moreextrema of said heart rate derivative, three or more directions ofchange of said heart rate derivative, a number of positive phases, or anumber of negative phases, provided the total number of positive phasesand negative phases is two or more.

In another aspect of the present disclosure, a method for indicating anoccurrence of a state change is provided. In one aspect of the presentdisclosure, the method comprises obtaining data relating to at least aportion of a heart beat complex from a patient; comparing said at leastsaid portion of said heart beat complex with a corresponding portion ofa reference heart beat complex template of said patient; and indicatingan occurrence of a state change based upon a determination that saidheart beat complex fails to match said reference heart beat complextemplate.

In yet another aspect of the present disclosure, a computer readableprogram storage device is provided that is encoded with instructionsthat, when executed by a computer, perform a method described above.

In one aspect of the present disclosure, a medical device is providedcomprising a computer readable program storage device as describedabove.

SUMMARY OF THE DISCLOSURE

In one aspect, the present disclosure relates to a method of treating apatient having epilepsy comprising receiving at least one body datastream, analyzing the at least one body data stream using a seizure orevent detection algorithm to detect whether or not the patient is havingand/or has had an epileptic seizure, receiving a cardiac signal of thepatient, applying a first electrical signal to a vagus nerve of thepatient based on a determination that the patient is not having and/orhas not had an epileptic seizure characterized by a decrease in thepatient's heart rate, wherein the first electrical signal is not a vagusnerve conduction blocking electrical signal, and applying a secondelectrical signal to a vagus nerve of the patient based on adetermination that the patient is having and/or has had an epilepticseizure characterized by a decrease in the patient's heart rate, whereinthe second electrical signal is a pulsed electrical signal that blocksaction potential conduction in the vagus nerve.

In one aspect, the present disclosure relates to a method of treating apatient having epilepsy comprising sensing a cardiac signal and akinetic signal of the patient, analyzing at least one of the cardiacsignal and the kinetic signal; determining whether or not the patienthas had an epileptic seizure based on the analyzing; in response to adetermination that the patient has had an epileptic seizure, determiningwhether or not the seizure is characterized by a decrease in thepatient's heart rate, applying a first electrical signal to a vagusnerve of the patient based on a determination that the patient has hadan epileptic seizure characterized by a decrease in the patient's heartrate, wherein the first electrical signal is a pulsed electrical signalthat blocks action potential conduction in the vagus nerve; and applyinga second electrical signal to a vagus nerve of the patient based on oneof a) a determination that the patient has not had an epileptic seizure,and b) a determination that the patient has had an epileptic seizurethat is not characterized by a decrease in the patient's heart rate,wherein the second electrical signal is not a vagus nerve conductionblocking electrical signal.

In one aspect, the present disclosure relates to a system for treating amedical condition in a patient, comprising at least one electrodecoupled to a vagus nerve of the patient, a programmable electricalsignal generator, a sensor for sensing at least one body data stream, aseizure detection module capable of analyzing the at least one body datastream and determining, based on the analyzing, whether or not thepatient is having and/or has had an epileptic seizure, a heart ratedetermination unit capable of determining a heart rate of a patientproximate in time to an epileptic seizure detected by the seizuredetection module, and a logic unit for applying a first electricalsignal to the vagus nerve using the at least one electrode based on adetermination by the seizure detection module that the patient is havingand/or has had an epileptic seizure characterized by a decrease in thepatient's heart rate, wherein the first electrical signal is a pulsedelectrical signal that blocks action potential conduction in the vagusnerve, and for applying a second electrical signal to the vagus nerveusing the at least one electrode as a cathode based upon one of a) adetermination that the patient is not having and/or has not had anepileptic seizure, and b) a determination that the patient is havingand/or has had an epileptic seizure that is not characterized by adecrease in the patient's heart rate, wherein the second electricalsignal is not a vagus nerve conduction blocking electrical signal. Inone embodiment, the seizure detection module may comprise the heart ratedetermination unit.

In one aspect, the present disclosure relates to a method of treating apatient having epilepsy comprising applying a first electrical signal toa vagus nerve of the patient, wherein the first electrical signal is anopen-loop electrical signal having a programmed on-time and a programmedoff-time, sensing at least one body signal of the patient, determiningthe start of an epileptic seizure based on the at least one body signal,determining whether or not the seizure is characterized by a decrease inthe patient's heart rate, applying a second, closed-loop electricalsignal to a vagus nerve of the patient based on a determination that theepileptic seizure is not characterized by a decrease in the patient'sheart rate, and applying a third, closed-loop electrical signal to avagus nerve of the patient based on a determination that the seizure ischaracterized by a decrease in the patient's heart rate, wherein thethird electrical signal is applied to block action potential conductionon the vagus nerve.

In one aspect, the present disclosure relates to a method of controllinga heart rate of an epilepsy patient comprising sensing a kinetic signalof the patient; analyzing said kinetic signal to determine at least onekinetic index; receiving a cardiac signal of the patient; analyzing thecardiac signal to determine the patient's heart rate; determining if thepatient's heart rate is commensurate with the at least one kineticindex; and applying a first electrical signal to a vagus nerve of thepatient based on a determination that the patient's heart rate is notcommensurate with the kinetic index. In one embodiment, the at least onekinetic index comprises at least one of an activity level or an activitytype of the patient, and determining if the heart rate is commensuratewith the kinetic index comprises determining if the heart rate iscommensurate with the at least one of an activity level or an activitytype.

In one aspect, the present disclosure relates to a method of controllinga heart rate of an epilepsy patient comprising sensing at least one of akinetic signal and a metabolic (e.g., oxygen consumption) signal of thepatient; receiving a cardiac signal of the patient; analyzing thecardiac signal to determine the patient's heart rate; determining if thepatient's heart rate is commensurate with the at least one of a kineticand a metabolic signal of the patient; and applying a first electricalsignal to a vagus nerve of the patient based on a determination that thepatient's heart rate is not commensurate with the at least one of akinetic signal and a metabolic signal. In one embodiment, the methodfurther comprises determining at least one of an activity level or anactivity type of the patient based on the at least one of a kinetic anda metabolic signal, and determining if the heart rate is commensuratewith the kinetic signal comprises determining if the heart rate iscommensurate with the at least one of an activity level or an activitytype.

In one aspect, the present disclosure relates to a method of treating apatient having epilepsy comprising sensing at least one body signal ofthe patient; determining whether or not the patient is having or has hadan epileptic seizure based on the at least one body signal; sensing acardiac signal of the patient; determining whether or not the seizure isassociated with a change in the patient's cardiac signal; applying afirst therapy to a vagus nerve of the patient based on a determinationthat the patient is having or has had an epileptic seizure that is notassociated with a change in the patient's cardiac signal, wherein thefirst therapy is selected from an electrical, chemical, mechanical(e.g., pressure) or thermal signal. The method further comprisesapplying a second therapy to a vagus nerve of the patient based on adetermination that the patient has had an epileptic seizure associatedwith a change in the patient's cardiac signal, wherein the secondtherapy is selected from an electrical, chemical, mechanical (e.g.,pressure) or thermal signal. In some embodiments, a third therapy may beapplied to a vagus nerve based a determination that the patient has nothad an epileptic seizure, wherein the third therapy is selected form anelectrical, chemical, mechanical or thermal signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIGS. 1A-1E provide stylized diagrams of an implantable medical deviceimplanted into a patient's body for providing first and secondelectrical signals to a vagus nerve of a patient for treating epilepticseizures, in accordance with one illustrative embodiment of the presentdisclosure;

FIG. 2 illustrates a block diagram depiction of an implantable medicaldevice of FIG. 1, in accordance with one illustrative embodiment of thepresent disclosure;

FIG. 3 illustrates a block diagram depiction of an electrode polarityreversal unit shown in FIG. 2, in accordance with one illustrativeembodiment of the present disclosure;

FIG. 4 illustrates a flowchart depiction of a method for providing firstand second electrical signals to a main trunk and a cardiac branch of avagus nerve, respectively, based upon whether or not the patient ishaving and/or has had an epileptic seizure, in accordance with anillustrative embodiment of the present disclosure;

FIG. 5 illustrates a flowchart depiction of a method for providing firstand second electrical signals to a main trunk and a cardiac branch of avagus nerve, respectively, based upon whether or not at least one of acardiac signal and a kinetic signal indicates that the patient is havingand/or has had an epileptic seizure, and whether the seizure ischaracterized by an increase in heart rate, in accordance with anillustrative embodiment of the present disclosure;

FIG. 6 illustrates a flowchart depiction of a method for providing afirst, open-loop electrical signal to a main trunk of a vagus nerve, asecond, closed-loop electrical signal to the main trunk of the vagusnerve based upon the patient having had an epileptic seizure notcharacterized by an increase in heart rate, and a third, closed-loopelectrical signal to a cardiac branch of a vagus nerve based upon thepatient having had an epileptic seizure characterized by an increase inheart rate, in accordance with an illustrative embodiment of the presentdisclosure; and

FIG. 7 is a flowchart depiction of a method for providing closed-loopvagus nerve stimulation for a patient with epilepsy by stimulating aright vagus nerve in response to detecting a seizure with tachycardiaand stimulating a left vagus nerve in the absence of such a detection.For example if a recumbent person's heart rate is 55 bpm and itincreases to 85 during a seizure, this is not clinical/pathologicaltachycardia, but may be considered tachycardia within the meaning ofsome embodiments of the present disclosure.

FIG. 8 is a flowchart depiction of a method for providing a closed-looptherapy to a vagus nerve of a patient with epilepsy in response todetecting a seizure associated with a heart rate decrease, wherein saidtherapy blocks impulse conduction along at least one vagus nerve.

FIG. 9 is a flowchart depicting a method for providing closed-loop vagusnerve stimulation based on an assessment of whether the patient's heartrate is commensurate with the patient's activity level or activity type.

FIG. 10 is a flowchart depicting a method for providing closed-loopvagus nerve stimulation based on a determination that the patient'sheart rate is incommensurate with the patient's activity level oractivity type, and further in view of whether the incommensurate changesinvolves relative tachycardia or relative bradycardia.

FIG. 11 is a graph of heart rate versus time, according to oneembodiment.

FIG. 12 is another graph of heart rate versus time, according to oneembodiment.

FIG. 13 is another graph of heart rate versus time, according to oneembodiment.

FIG. 14 is another graph of heart rate versus time, according to oneembodiment.

FIG. 15 is another graph of heart rate versus time, according to oneembodiment.

FIG. 16 is a flowchart of a therapy procedure, according to oneembodiment.

FIG. 17 is a graph relating to the automated detection and control ofictal and peri-ictal chronotropic instability, according to oneembodiment.

FIG. 18 is a graph relating to the automated detection and control ofictal and peri-ictal chronotropic instability, according to oneembodiment.

FIG. 19 is a graph relating to the automated detection and control ofictal and peri-ictal chronotropic instability, according to oneembodiment.

FIG. 20 is a graph relating to the automated detection and control ofictal and peri-ictal chronotropic instability, according to oneembodiment.

FIG. 21 is a graph relating to the automated detection and control ofictal and peri-ictal chronotropic instability, according to oneembodiment.

FIG. 22 provides a stylized diagram of a medical device implanted into apatient's body for providing a therapeutic electrical signal to a neuralstructure of the patient's body, in accordance with one illustrativeembodiment of the present disclosure;

FIG. 23A is a block diagram of a medical device system that includes amedical device and an external unit, in accordance with one illustrativeembodiment of the present disclosure;

FIG. 23B is a block diagram of a medical device system that includes amedical device and an external unit, in accordance with one illustrativeembodiment of the present disclosure;

FIG. 24A is a stylized block diagram of a cardiac data collection moduleof a medical device, in accordance with one illustrative embodiment ofthe present disclosure; 100591 FIG. 24B is a stylized block diagram of aheart beat/interval determination module of a medical device, inaccordance with one illustrative embodiment of the present disclosure;

FIG. 24C is a stylized block diagram of a HR derivative/complex moduleof a medical device, in accordance with one illustrative embodiment ofthe present disclosure;

FIG. 24D is a stylized block diagram of a template match module of amedical device, in accordance with one illustrative embodiment of thepresent disclosure;

FIG. 25 illustrates a flowchart depiction of a method for detecting astate change and taking one or more responsive actions, in accordancewith an illustrative embodiment of the present disclosure;

FIG. 26 shows basic shapes of a heart rate plot, from which more complexshapes can be produced by deformation in accordance with an illustrativeembodiment of the present disclosure;

FIG. 27 shows a graph of heart rate (BPM) vs. time (hr), with anepileptic event identified by electrocorticography (ECoG) indicated byvertical lines, from which a triangle pattern is discernible, inaccordance with an illustrative embodiment of the present disclosure;

FIG. 28A shows a graph of heart rate vs. time, with epileptic eventsidentified by ECoG indicated by vertical lines, from each of which anotched triangle pattern is discernible, in accordance with anillustrative embodiment of the present disclosure;

FIG. 28B shows a graph of heart rate vs. time, with epileptic eventsidentified by ECoG indicated by vertical lines, from each of which anotched triangle pattern is discernible, in accordance with anillustrative embodiment of the present disclosure;

FIG. 28C shows a graph of heart rate vs. time, with epileptic eventsidentified by ECoG indicated by vertical lines, from each of which anotched triangle pattern is discernible, in accordance with anillustrative embodiment of the present disclosure;

FIG. 29A shows a graph of heart rate vs. time, with epileptic eventsidentified by ECoG indicated by vertical lines, from which an “M”pattern is discernible, in accordance with an illustrative embodiment ofthe present disclosure;

FIG. 29B shows a graph of heart rate vs. time, with epileptic eventsidentified by ECoG indicated by vertical lines, from which an “M”pattern is discernible, in accordance with an illustrative embodiment ofthe present disclosure;

FIG. 29C shows a graph of heart rate vs. time, with epileptic eventsidentified by ECoG indicated by vertical lines, from which an “M”pattern is discernible, in accordance with an illustrative embodiment ofthe present disclosure;

FIG. 30 shows a graph of heart rate vs. time, with an epileptic eventidentified by ECoG indicated by vertical lines, from which a “W” patternis discernible, in accordance with an illustrative embodiment of thepresent disclosure;

FIG. 31 shows a graph of heart rate vs. time, with an epileptic eventidentified by ECoG indicated by vertical lines, from which a fused “M”and “W” pattern is discernible, in accordance with an illustrativeembodiment of the present disclosure;

FIG. 32A shows a graph of heart rate vs. time, with epileptic eventsidentified by ECoG indicated by vertical lines, from which a pattern ofperiodic oscillations is discernible, in accordance with an illustrativeembodiment of the present disclosure;

FIG. 32B shows a graph of heart rate vs. time, with epileptic eventsidentified by ECoG indicated by vertical lines, from which a pattern ofperiodic oscillations is discernible, in accordance with an illustrativeembodiment of the present disclosure;

FIG. 33 shows a graph of heart rate vs. time, with an epileptic eventidentified by ECoG indicated by vertical lines, from which a pattern ofperiodic oscillations, specifically forming a sawtooth pattern, isdiscernible, in accordance with an illustrative embodiment of thepresent disclosure;

FIG. 34A shows a graph of heart rate vs. time, with epileptic eventsidentified by ECoG indicated by vertical lines, from which a pattern ofperiodic oscillations overlaid on a longer-timescale triangle pattern isdiscernible, in accordance with an illustrative embodiment of thepresent disclosure;

FIG. 34B shows a graph of heart rate vs. time, with epileptic eventsidentified by ECoG indicated by vertical lines, from which a pattern ofperiodic oscillations overlaid on a longer-timescale triangle pattern isdiscernible, in accordance with an illustrative embodiment of thepresent disclosure;

FIG. 34C shows a graph of heart rate vs. time, with epileptic eventsidentified by ECoG indicated by vertical lines, from which a pattern ofperiodic oscillations overlaid on a longer-timescale triangle pattern isdiscernible, in accordance with an illustrative embodiment of thepresent disclosure;

FIG. 34D shows a graph of heart rate vs. time, with epileptic eventsidentified by ECoG indicated by vertical lines, from which a pattern ofperiodic oscillations overlaid on a longer-timescale triangle pattern isdiscernible, in accordance with an illustrative embodiment of thepresent disclosure;

FIG. 35 shows a graph of heart rate vs. time, with an epileptic eventidentified by ECoG indicated by vertical lines, from which periodicoscillations forming a “comb” pattern are discernible, as well as apattern of lower amplitude periodic oscillations overlaid on alonger-timescale triangle pattern is discernible, in accordance with anillustrative embodiment of the present disclosure;

FIG. 36 shows a graph of heart rate vs. time, with an epileptic eventidentified by ECoG indicated by vertical lines, from which a pattern ofperiodic oscillations overlaid on a longer-timescale parabola pattern isdiscernible, in accordance with an illustrative embodiment of thepresent disclosure;

FIG. 37 shows a graph of heart rate vs. time, with an epileptic eventidentified by ECoG indicated by vertical lines, from which a triphasicpattern is discernible, in accordance with an illustrative embodiment ofthe present disclosure;

FIG. 38A shows a graph of heart rate vs. time, with epileptic eventsidentified by ECoG indicated by vertical lines, from which multiple “M”and/or “W” patterns are discernible, in accordance with an illustrativeembodiment of the present disclosure;

FIG. 38B shows a graph of heart rate vs. time, with epileptic eventsidentified by ECoG indicated by vertical lines, from which multiple “M”and/or “W” patterns are discernible, in accordance with an illustrativeembodiment of the present disclosure;

FIG. 39 shows exemplary heart beat complex changes detectable by use ofthe P wave and the R wave of a heart beat, in accordance with anillustrative embodiment of the present disclosure; and

FIGS. 40A-B show a first heart beat complex derived from data collectedover an entire period of EKG monitoring of a patient (A) and a secondheart beat complex derived from EKG data collected from the same patientduring circumictal periods only (B).

While the disclosure is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the disclosure to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the disclosure as defined by the appended claims.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Illustrative embodiments of the disclosure are described herein. Forclarity, not all features of an actual implementation are provided indetail. In any actual embodiment, numerous implementation-specificdecisions must be made to achieve the design-specific goals. Such adevelopment effort, while possibly complex and time-consuming, wouldnevertheless be a routine task for persons of skill in the art giventhis disclosure.

This application does not intend to distinguish between components thatdiffer in name but not function. “Including” and “includes” are used inan open-ended fashion, and should be interpreted to mean “including, butnot limited to.” “Couple” or “couples” are intended to mean either adirect or an indirect electrical connection. “Direct contact,” “directattachment,” or providing a “direct coupling” indicates that a surfaceof a first element contacts the surface of a second element with nosubstantial attenuating medium there between. Small quantities ofsubstances, such as bodily fluids, that do not substantially attenuateelectrical connections do not vitiate direct contact. “Or” is used inthe inclusive sense (i.e., “and/or”) unless a specific use to thecontrary is explicitly stated.

“Electrode” or “electrodes” may refer to one or more stimulationelectrodes (i.e., electrodes for applying an electrical signal generatedby an IMD to a tissue), sensing electrodes (i.e., electrodes for sensinga body signal), and/or electrodes capable of either stimulation orsensing. “Cathode” and “anode” have their standard meanings, as theelectrode at which current leaves the IMD system and the electrode atwhich current enters the IMD system, respectively. Reversing thepolarity of the electrodes can be effected by any switching techniqueknown in the art.

A “pulse” is used herein to refer to a single application of electricalcharge from the cathode to target neural tissue. A pulse may includeboth a therapeutic portion (in which most or all of the therapeutic oraction-potential-generating effect occurs) and a charge-balancingportion in which the polarity of the electrodes are reversed and theelectrical current is allowed to flow in the opposite direction to avoidelectrode and/or tissue damage. Individual pulses are separated by atime period in which no charge is delivered to the nerve, which can becalled the “interpulse interval.” A “burst” is used herein to refer to aplurality of pulses, which may be separated from other bursts by aninterburst interval in which no charge is delivered to the nerve. Theinterburst intervals have a duration exceeding the interpulse intervalduration. In one embodiment, the interburst interval is at least twiceas long as the interpulse interval. The time period between the end ofthe last pulse of a first burst and the initiation of the first pulse ofthe next subsequent burst can be called the “interburst interval.” Inone embodiment, the interburst interval is at least 100 msec.

A plurality of pulses can refer to any of (a) a number of consecutivepulses within a burst, (b) all the pulses of a burst, or (c) a number ofconsecutive pulses including the final pulse of a first burst and thefirst pulse of the next subsequent burst.

“Stimulate,” “stimulating” and “stimulator” may generally refer toapplying a signal, stimulus, or impulse to neural tissue (e.g., a volumeof neural tissue in the brain or a nerve) for affecting it neuronalactivity. While the effect of such stimulation on neuronal activity istermed “modulation,” for simplicity, the terms “stimulating” and“modulating”, and variants thereof, are sometimes used interchangeablyherein. The modulation effect of a stimulation signal on neural tissuemay be excitatory or inhibitory, and may potentiate acute and/orlong-term changes in neuronal activity. For example, the modulationeffect of a stimulation signal may comprise: (a) initiating actionpotentials in the target neural tissue; (b) inhibition of conduction ofaction potentials (whether endogenous or exogenously generated, orblocking their conduction (e.g., by hyperpolarizing or collisionblocking), (c) changes in neurotransmitter/neuromodulator release oruptake, and (d) changes in neuroplasticity or neurogenesis of braintissue. Applying an electrical signal to an autonomic nerve may comprisegenerating a response that includes an afferent action potential, anefferent action potential, an afferent hyperpolarization, an efferenthyperpolarization, an afferent sub-threshold depolarization, and/or anefferent sub-threshold depolarization. The terms tachycardia andbradycardia are used here in a relative (i.e., any decrease or decreasein heart rate relative to a reference value) or in an absolute sense(i.e., a pathological change relative to a normative value). Inparticular, “tachycardia is used interchangeably with an increase heartrate and “bradycardia” may be used interchangeably with a decrease inheart rate.

A variety of stimulation therapies may be provided in embodiments of thepresent disclosure. Different nerve fiber types (e.g., A, B, andC-fibers that may be targeted) respond differently to stimulation fromelectrical signals because they have different conduction velocities andstimulation threshold. Certain pulses of an electrical stimulationsignal, for example, may be below the stimulation threshold for aparticular fiber and, therefore, may generate no action potential. Thus,smaller or narrower pulses may be used to avoid stimulation of certainnerve fibers (such as C-fibers) and target other nerve fibers (such as Aand/or B fibers, which generally have lower stimulation thresholds andhigher conduction velocities than C-fibers). Additionally, techniquessuch as a pre-pulse may be employed wherein axons of the target neuralstructure may be partially depolarized (e.g., with a pre-pulse orinitial phase of a pulse) before a greater current is delivered to thetarget (e.g., with a second pulse or an initial phase such a stair steppre-pulse to deliver a larger quantum of charge). Furthermore, opposingpolarity phases separated by a zero current phase may be used to exciteparticular axons or postpone nerve fatigue during long term stimulation.

Cranial nerve stimulation, such as vagus nerve stimulation (VNS), hasbeen proposed to treat a number of medical conditions, includingepilepsy and other movement disorders, depression and otherneuropsychiatric disorders, dementia, traumatic brain injury, coma,migraine headache, obesity, eating disorders, sleep disorders, cardiacdisorders (such as congestive heart failure and atrial fibrillation),hypertension, endocrine disorders (such as diabetes and hypoglycemia),and pain, among others. See, e.g., U.S. Pat. Nos. 4,867,164; 5,299,569;5,269,303; 5,571,150; 5,215,086; 5,188,104; 5,263,480; 6,587,719;6,609,025; 5,335,657; 6,622,041; 5,916,239; 5,707,400; 5,231,988; and5,330,515. Despite the variety of disorders for which cranial nervestimulation has been proposed or suggested, the fact that detailedneural pathways for many (if not all) cranial nerves remain relativelyunknown, makes predictions of efficacy for any given disorder difficultor impossible. Even if such pathways were known, the precise stimulationparameters that would modulate particular pathways relevant to aparticular disorder generally cannot be predicted.

Cardiac signals suitable for use in embodiments of the presentdisclosure may comprise one or more of an electrical (e.g., EKG),acoustic (e.g., phonocardiogram or ultrasound/ECHO), force or pressure(e.g., apexcardiogram), arterial pulse pressure and waveform or thermalsignals that may be recorded and analyzed to extract features such asheart rate, heart rate variability, rhythm (regular, irregular, sinus,ventricular, ectopic, etc.), morphology, etc.

It appears that sympatho-vagal imbalance (lower vagal and highersympathetic tone) plays an important role in generation of a widespectrum of ictal and interictal alterations in cardiac dynamics,ranging from rare unifocal PVCs to cardiac death. Without being bound bytheory, restoration of the vagal tone to a level sufficient tocounteract the pathological effects of elevated catecholamines may servea cardio-protective purpose that would be particularly beneficial inpatients with pharmaco-resistant epilepsies, who are at highest risk forSUDEP.

In one embodiment, the present disclosure provides methods and apparatusto increase cardiac vagal tone in epilepsy patients by timely deliveringtherapeutic electrical currents to the trunks of the right or left vagusnerves or to their cardiac rami (branches), in response to increases insympathetic tone, by monitoring among others, heart rate, heart rhythm,EKG morphology, blood pressure, skin resistance, catecholamine or theirmetabolites and neurological signals such as EEG/ECoG, kinetic (e.g.,amplitude velocity, direction of movements) and cognitive (e.g., complexreaction time).

In one embodiment, the present disclosure provides a method of treatinga medical condition selected from the group consisting of epilepsy,neuropsychiatric disorders (including but not limited to depression),eating disorders/obesity, traumatic brain injury, addiction disorders,dementia, sleep disorders, pain, migraine, endocrine/pancreaticdisorders (including but not limited to diabetes), motility disorders,hypertension, congestive heart failure/cardiac capillary growth, hearingdisorders, angina, syncope, vocal cord disorders, thyroid disorders,pulmonary disorders, gastrointestinal disorders, kidney disorders, andreproductive endocrine disorders (including infertility).

FIGS. 1A-1E depict a stylized implantable medical system 100 forimplementing one or more embodiments of the present disclosure. FIGS. 1Aand 1B illustrate an electrical signal generator 110 having main body112 comprising a case or shell (commonly referred to as a “can”) 121)(FIG. 1B) with a header 116 for connecting to a lead assembly 122. Anelectrode assembly 125, preferably comprising at least an electrodepair, is conductively connected to the distal end of an insulated,electrically conductive lead assembly 122, which preferably comprises aplurality of lead wires (at least one wire for each electrode of theelectrode assembly 125). Lead assembly 122 is attached at its proximalend to one or more connectors on header 116 (FIG. 1B).

Electrode assembly 125 may be surgically coupled to a target tissue fordelivery of a therapeutic electrical signal, which may be a pulsedelectrical signal. The target tissue may be a cranial nerve, such as avagus nerve 127 (FIGS. 1A, 1C-E) or another cranial nerve such as atrigeminal nerve. Electrode assembly 125 includes one or more electrodes125-1, 125-2, 125-3, which may be coupled to the target tissue. Theelectrodes may be made from any of a variety of conductive metals knownin the art, e.g., platinum, iridium, oxides of platinum or iridium, orcombinations of the foregoing. In one embodiment, the target tissue is avagus nerve 127, which may include an upper main trunk portion 127-1above a cardiac branch 127-2, and a lower main trunk portion 127-3 belowthe cardiac branch.

In one embodiment, at least one electrode may be coupled to the maintrunk of the vagus nerve, and at least one electrode 125-2 may becoupled to a cardiac branch 127-2 of the vagus nerve (FIG. 1C). The atleast one main trunk electrode may be coupled to an upper main trunk127-1 (e.g., electrode 125-1, FIG. 1C) or a lower main trunk 127-3(e.g., electrode 125-3). The at least one main trunk electrode (125-1,125-3) may be used as a cathode to provide a first electrical signal tothe upper (127-1) or lower (127-3) main trunk. Cardiac branch electrode125-2 may be used as a cathode to provide a second electrical signal tocardiac branch 127-2. An additional electrode to function as the anodemay be selected from one or more of the other electrodes in electrodeassembly 125, can 121, or a dedicated anode.

In some embodiments (FIGS. 1D, 1E), electrode assembly 125 may include amain trunk electrode pair comprising a cathode 125-1 a and an anode125-1 b for coupling to a main trunk of a vagus nerve 127. The maintrunk electrode pair 125-1 a, 125-1 b may be coupled to an upper maintrunk 127-1 of a vagus nerve (FIG. 1D), or to a lower main trunk 127-3(FIG. 1E) for delivering a first electrical signal. Without being boundby theory, it is believed that few or no vagal afferent fibers in thelower main trunk 127-3 pass into cardiac branch 127-2 and, accordingly,that effects of the first electrical signal on cardiac function may beminimized by coupling electrode pair 125-1 a and 125-1 b to the lowermain trunk 127-3 instead of upper main trunk 127-1. Cardiac effects mayalso be minimized by alternative embodiments in which the firstelectrical signal is applied to a lower main trunk 127-3 using a singleelectrode (e.g., 125-3, FIG. 1C) as a cathode and an anode that is notcoupled to the vagus nerve 127 (e.g., by using can 121 as an anode).

In some embodiments (FIGS. 1D, 1E), electrode assembly 125 may include acardiac branch electrode pair comprising a cathode 125-2 a and an anode125-2 b for coupling to a cardiac branch of a vagus nerve. The secondcardiac branch electrode pair may be used to provide a second electricalsignal to a cardiac branch of the nerve to affect the cardiac functionof the patient.

Referring again to FIGS. 1C-1E, a first electrical signal may beprovided to generate afferent action potentials in a main trunk of avagus nerve to modulate electrical activity of the patient's brainwithout significantly affecting the patient's heart rate. The secondelectrical signal may generate efferent action potentials to module thecardiac activity of the patient, and in particular to slow the patient'sheart rate (e.g., to treat an epilepsy patient having seizurescharacterized by ictal tachycardia) and maintain or restore asympathetic/parasympathetic balance to a non-pathological state. Thefirst electrical signal may be applied to the main trunk of the vagusnerve in a variety of ways, so long as at least one electrode is coupledto the main trunk as a cathode. As noted, the cathode may be coupled toeither an upper (127-1) or lower (127-3) main trunk, and an anode may beprovided by any of the other electrodes on the vagus nerve (e.g., 125-1b, 125-2 b, 125-3, FIGS. 1C-1E) or by a separate anode not coupled tothe vagus nerve (e.g., can 121). In one alternative embodiment, anelectrode 125-3 may be coupled to a lower main trunk 127-3 of the vagusnerve to function as an anode. In yet another embodiment, eachindividual electrode element in FIGS. 1A-E (e.g., 125-1, 125-2, 125-3,125-1 a, 125-1 g, 125-2 a, 125-2 b) may comprise an electrode paircomprising both an anode and a cathode. In an additional embodiment,each individual electrode element may comprise three electrodes (e.g.,one serving as cathode and the other two as anodes). Suitable electrodeassemblies are available from Cyberonics, Inc., Houston, Tex., USA asthe Model 302, PerenniaFlex and PerenniaDura electrode assemblies. Inview of the present disclosure, persons of skill in the art willappreciate that many electrode designs could be used in embodiments ofthe present disclosure including unipolar electrodes.

Embodiments of the present disclosure may comprise electrical signalswith either charge-balanced or non-charge-balanced pulses (e.g.,monopolar/monophasic, direct current (DC)). Charge-balanced pulsesinvolve a first phase in which the stimulation occurs (i.e., actionpotentials are induced in target nerve fibers), and a second phase inwhich the polarity of the electrodes are reversed (i.e., the stimulationphase cathode becomes the charge-balancing phase anode, and vice versa).The result is a pulse having two opposite-polarity phases of equalcharge, such that no net charge flows across the electrode during apulse. Charge-balancing is often used to avoid damage to the electrodesthat may result if a pulse results in a net charge flowing across theelectrodes.

In some instances, charge-balancing may involve a passive dischargephase as illustrated in, e.g., FIG. 1A of US Publication 2006/0173493,which is hereby incorporated by reference in its entirety. In passivecharge-balancing, the charge-balancing phase typically involves allowinga capacitor having a charge equal to the charge applied to the nerveduring the stimulation phase to discharge through the polarity-reversedelectrodes. Passive charge-balancing typically uses much lower initialcurrent than the stimulation phase, with the current declining to zeroover a much longer time period than the pulse width of the stimulationphase. A lower current is typically selected in the charge-balancingphase so as to avoid or minimize nerve recruitment during thecharge-balancing phase. In active charge-balancing, the charge-balancingphase is not accomplished by the passive discharge of a capacitor, butby providing a second phase having an opposite polarity but the samecharge magnitude (pulse width multiplied by current) as the first phase.As is usually the case with passive charge-balancing, activecharge-balancing typically involves a much lower current that is appliedover a longer time period than the stimulation phase, so as to avoidnerve recruitment. In some instances, however, the activecharge-balancing phase may be used as a second stimulation phase byselecting a current magnitude of the cathode in the charge-balancingphase (typically a second electrode, which may be the anode of theinitial stimulation phase) that is sufficient to generate actionpotentials in nerve fibers of the target tissue.

Embodiments of the present disclosure may be implemented using passivecharge balancing or active charge-balancing, and the latter may beprovided as a stimulation phase or a non-stimulation phase. Someembodiments may be implemented with non-charge-balanced pulses. Personsof skill in the art, having the benefit of the present disclosure, mayselect the type of charge balancing (if desired) based upon a number offactors including but not limited to whether or not the charge-balancingis intended to affect the cardiac cycle or not, whether afferent orefferent stimulation is desired, the number and location of availableelectrodes for applying the electrical signal, the fibers intended to berecruited during a particular phase and their physiological effects,among many other factors.

In the discussion of electrical signals in the present disclosure,unless otherwise stated, references to electrodes as cathodes or anodesrefers to the polarities of the electrodes during a stimulation phase ofa pulse, whether the pulse is a charge-balanced pulse or anon-charge-balanced pulse (e.g., monopolar/monophasic or DC). It will beappreciated that where charge-balanced pulses are employed, thepolarities will be reversed during a charge-balancing phase. Whereactive charge-balancing is used, cardiac effects may be furtheramplified or ameliorated, depending upon the location of the electrodesbeing used.

Returning to FIG. 1A, in some embodiments, a heart rate sensor 130,and/or a kinetic sensor 140 (e.g., a triaxial accelerometer) may beincluded in the system 100 to sense one or more of a cardiac signal ordata stream and a kinetic data stream of the patient. In one embodiment,the heart rate sensor may comprise a separate element 130 that may becoupled to generator 110 through header 116 as illustrated in FIG. 1A.In another embodiment, the electrodes 125-1, 125-2, 125-3 and/or the can121 may be used as sensing electrodes to sense heart rate. Anaccelerometer may be provided inside generator 110 in one embodiment tosense a kinetic signal (e.g., body movement) of the patient. One or moreof the heart rate sensor 130 and the kinetic sensor 140 may be used by aseizure detection algorithm in the system 100 to detect epilepticseizures. In alternative embodiments, other body signals (e.g., bloodpressure, brain activity, blood oxygen/CO₂ concentrations, temperature,skin resistivity, etc.) of the patient may be sensed and used by theseizure detection algorithm to detect epileptic seizures. Signalgenerator 110 may be implanted in the patient's chest in a pocket orcavity formed by the implanting surgeon below the skin (indicated byline 145, FIG. 1A).

Returning to FIGS. 1A and 1C, a first electrode 125-1 may be wrapped orotherwise electrically coupled to an upper main trunk 127-1 of a vagusnerve 127 of the patient, and a second electrode 125-2 may be wrapped orcoupled to a cardiac branch 127-2 of the vagus nerve. In one embodiment,a third electrode 125-3 may be coupled to a lower main trunk 127-3 ofthe vagus nerve below the cardiac branch 127-2 of the vagus nerve,instead of or in addition to first electrode 125-1 coupled to the uppermain trunk above the cardiac branch. In some embodiments, thirdelectrode 125-3 may be omitted. Electrode assembly 125 may be secured tothe nerve by a spiral anchoring tether 128 (FIG. 1C), which in oneembodiment does not include an electrode but in alternative embodimentsmay contain up to three electrodes that serve as cathode(s) and anode(s)in any possible combination. Lead assembly 122 may further be secured,while retaining the ability to flex, by a suture connection 130 tonearby tissue (FIG. 1C). In particular embodiments, any of first, secondand third electrodes 125-1, 125-2, and 125-3 may be used as either acathode or as an anode. In general, the foregoing electrodes may be usedas a cathode when the particular electrode is the closest electrode(among a plurality of electrodes) to the target organ (e.g., heart,brain, stomach, liver, etc.) to be stimulated. While a single electrode(e.g., 125-1, 125-2, or 125-3) is illustrated in connection with uppermain trunk 127-1, cardiac branch 127-2, and lower main trunk 127-3 inFIGS. 1A and 1C for simplicity, it will be appreciated that one or moreadditional electrodes can be provided on each of the foregoing neuralstructures to provide greater flexibility in stimulation.

In one embodiment, the open helical design of the electrodes 125-1,125-2, 125-3, is self-sizing, flexible, minimize mechanical trauma tothe nerve and allow body fluid interchange with the nerve. The electrodeassembly 125 preferably conforms to the shape of the nerve, providing alow stimulation threshold by allowing a large stimulation contact areawith the nerve. Structurally, the electrode assembly 125 comprises anelectrode ribbon (not shown) for each of electrodes 125-1, 125-2, 125-3,made of a conductive material such as platinum, iridium,platinum-iridium alloys, and/or oxides thereof. The electrode ribbonsare individually bonded to an inside surface of an elastomeric bodyportion of the spiral electrodes 125-1, 125-2, 125-3 (FIG. 1C), whichmay comprise spiral loops of a multi-loop helical assembly. Leadassembly 122 may comprise three distinct lead wires or a triaxial cablethat are respectively coupled to one of the conductive electroderibbons. One suitable method of coupling the lead wires to theelectrodes 125-1, 125-2, 125-3 comprises a spacer assembly such as thatdisclosed in U.S. Pat. No. 5,531,778, although other known couplingmethods may be used.

The elastomeric body portion of each loop may be composed of siliconerubber or other biocompatible elastomeric compounds, and the fourth loop128 (which may have no electrode in some embodiments) acts as theanchoring tether for the electrode assembly 125.

In one embodiment, electrical pulse generator 110 may be programmed withan external computer 150 using programming software known in the art forstimulating neural structures, and a programming wand 155 to facilitateradio frequency (RF) communication between the external computer 150(FIG. 1A) and the implanted pulse generator 110. In one embodiment, wand155 and software permit wireless, non-invasive communication with thegenerator 110 after surgical implantation. Wand 155 may be powered byinternal batteries, and provided with a “power on” light to indicatesufficient power for communications. Another indicator light may beprovided to show that data transmission is occurring between the wandand the generator. In other embodiments, wand 155 may be omitted, e.g.,where communications occur in the 401-406 MHz bandwidth for MedicalImplant Communication Service (MICS band).

In some embodiments of the disclosure, a body data stream may beanalyzed to determine whether or not a seizure has occurred. Manydifferent body data streams and seizure detection indices have beenproposed for detecting epileptic seizures. Additional details on methodof detecting seizure from body data are provided in U.S. Pat. Nos.8,337,404 and 8,382,667, both issued in the name of the presentapplicant and both entitled, “Detecting, Quantifying, and/or ClassifyingSeizures Using Multimodal Data,” as well as in co-pending U.S. patentapplication Ser. No. 13/288,886, filed Nov. 3, 2011, each herebyincorporated by reference in its entirety herein. Seizure detectionbased on the patient's heart rate (as sensed by implanted or externalelectrodes), movement (as sensed by, e.g., a triaxial accelerometer),responsiveness, breathing, blood oxygen saturation, skinresistivity/conductivity, temperature, brain activity, and a number ofother body data streams are provided in the foregoing patents andco-pending applications.

In one embodiment, the present disclosure provides a method for treatinga patient with epilepsy in which a body data stream is analyzed using aseizure detection algorithm to determine whether or not the patient hashad an epileptic seizure. As used herein, the term “has had an epilepticseizure” includes instances in which a seizure onset has been detected,as well as instances in which the seizure onset has been detected andthe seizure is still ongoing (i.e., the seizure has not ended). If theanalysis results in a determination that the patient has not had anepileptic seizure, a signal generator may apply a first electricalsignal to a main trunk of a vagus nerve of the patient. If the analysisresults in a determination that the patient has had an epilepticseizure, the signal generator may apply a second electrical signal to acardiac branch of a vagus nerve of the patient. In some embodiments, theapplication of the first electrical signal to the main trunk isterminated, and only the second electrical signal to the cardiac branchis provided once a seizure is detected.

In alternative embodiments, both the first and second electrical signalsmay be applied to the main trunk and cardiac branch, respectively, ofthe vagus nerve in response to a determination that the patient has hada seizure (i.e., the first electrical signal continues to be applied tothe main trunk of the vagus nerve and the second signal is initiated).Where both the first and second electrical signals are provided, the twosignals may be provided sequentially, or in alternating fashion to themain trunk and the cardiac branch. In one embodiment, the first signalmay be provided to the main trunk by using one of the upper main trunkelectrode 125-1 or the lower main trunk electrode 125-3 as the cathodeand the cardiac branch electrode 125-2 as the anode, or by using both ofthe upper main trunk electrode and the lower main trunk electrode as thecathode and the anode. The second signal may be provided (e.g., byrapidly changing the polarity of the electrodes) by using the cardiacbranch electrode 125-2 as the cathode and a main trunk electrode 125-1or 125-3 as the anode.

In still other embodiments, the second electrical signal is applied tothe cardiac branch of the vagus nerve only if the analysis results in adetermination that the patient is having and/or has had an epilepticevent that is accompanied by an increase in heart rate, and the secondelectrical signal is used to lower the heart rate back towards a ratethat existed prior to the seizure onset. Without being bound by theory,the present inventors believe that slowing the heart rate at the onsetof seizures—particularly where the seizure is accompanied by an increasein heart rate—may improve the ability of VNS therapy to providecardio-protective benefits.

Prior patents describing vagus nerve stimulation as a medical therapyhave cautioned that undesired slowing of the heart rate may occur, andhave proposed various methods of avoiding such a slowing of the heartrate. In U.S. Pat. No. 6,341,236, it is suggested to sense heart rateduring delivery of VNS and if a slowing of the heart rate is detected,either suspending delivery of the VNS signal or pacing the heart using apacemaker. The present application discloses a VNS system that detectsepileptic seizures, particularly epileptic seizures accompanied by anincrease in heart rate, and intentionally applies an electrical signalto slow the heart rate in response to such a detection. In anotheraspect, the present application discloses VNS systems that provide afirst electrical signal to modulate only the brain during periods inwhich no seizure has been detected, and either 1) a second electricalsignal to modulate only the heart (to slow its rate) or 2) both a firstelectrical signal to the brain and a second electrical signal to theheart, in response to a detection of the onset of an epileptic seizure.These electrical signals may be delivered simultaneously, sequentially(e.g., delivery of stimulation to the brain precedes delivery ofstimulation to the heart or vice versa), or delivery of the first andsecond signals may be interspersed or interleaved.

The first electrode may be used as a cathode to provide an afferentfirst electrical signal to modulate the brain of the patient via maintrunk electrode 125-1. Electrode 125-1 may generate both afferent andefferent action potentials in vagus nerve 127. One or more of electrodes125-2 and 125-3 are used as anodes to complete the circuit. Where thisis the case, some of the action potentials may be blocked at theanode(s), with the result that the first electrical signal maypredominantly modulate the brain by afferent actions traveling towardthe brain, but may also modulate one or more other organs by efferentaction potentials traveling toward the heart and/or lower organs, to theextent that the efferent action potentials are not blocked by theanode(s).

The second electrode may be used as a cathode to provide an efferentsecond electrical signal to slow the heart rate of the patient viacardiac branch electrode 125-2. Either first electrode 125-1 or a thirdelectrode 125-3 (or can 121) may be used as an anode to complete thecircuit. In one embodiment, the first electrical signal may be appliedto the upper (127-1) or lower (127-3) main trunk of the vagus nerve inan open-loop manner according to programmed parameters including anoff-time and an on-time. The on-time and off-time together establish theduty cycle determining the fraction of time that the signal generatorapplies the first electrical. In one embodiment, the off-time may rangefrom 7 seconds to several hours or even longer, and the on-time mayrange from 5 seconds to 300 seconds. It should be noted that the dutycycle does not indicate when current is flowing through the circuit,which is determined from the on-time together with the pulse frequency(usually 10-200, Hz, and more commonly 20-30 Hz) and pulse width(typically 0.1-0.5 milliseconds). The first electrical signal may alsobe defined by a current magnitude (e.g., 0.25-3.5 milliamps), andpossibly other parameters (e.g., pulse width, and whether or not acurrent ramp-up and/or ramp-down is provided, a frequency, and a pulsewidth.

In one embodiment, a seizure detection may result in both applying thefirst electrical signal to provide stimulation to the brain in closeproximity to a seizure detection (which may interrupt or terminate theseizure), as well as application of the second electrical signal whichmay slow the heart, thus exerting a cardio-protective effect. In aparticular embodiment, the second electrical signal is applied only inresponse to a seizure detection that is characterized by (or accompaniedor associated with) an increase in heart rate, and is not applied inresponse to seizure detections that are not characterized by an increasein heart rate. In this manner, the second electrical signal may helpinterrupt the seizure by restoring the heart to a pre-seizure baselineheart rate when the patient experiences ictal tachycardia (elevatedheart rate during the seizure), while leaving the heart rate unchangedif the seizure has no significant effect on heart rate.

In still further embodiments, additional logical conditions may beestablished to control when the second electrical signal is applied tolower the patient's heart rate following a seizure detection. In oneembodiment, the second electrical signal is applied only if themagnitude of the ictal tachycardia rises above a defined level. In oneembodiment, the second electrical signal is applied to the cardiacbranch only if the heart rate increases by a threshold amount above thepre-ictal baseline heart rate (e.g., more than 20 beats per minute abovethe baseline rate). In another embodiment, the second electrical signalis applied to the cardiac branch only if the heart rate exceeds anabsolute heart rate threshold (e.g., 100 beats per minute, 120 beats perminute, or other programmable threshold). In a further embodiment, aduration constraint may be added to one or both of the heart rateincrease or absolute heart rate thresholds, such as a requirement thatthe heart rate exceed the baseline rate by 20 beats per minute for morethan 10 seconds, or exceed 110 beats per minute for more than 10seconds, before the second electrical signal is applied to the cardiacbranch in response to a seizure detection.

In another embodiment, the heart rate sensor continues to monitor thepatient's heart rate during and/or after application of the secondelectrical signal, and the second electrical signal is interrupted orterminated if the patient's heart rate is reduced below a low heart ratethreshold, which may be the baseline heart rate that the patientexperienced prior to the seizure, or a rate lower or higher than thebaseline pre-ictal heart rate. The low rate threshold may provide ameasure of safety to avoid undesired events such as bradycardia and/orsyncope.

In yet another embodiment, heart rate sensor 130 may continue to monitorheart rate and/or kinetic sensor 140 may continue to monitor bodymovement in response to applying the second electrical signal, and thesecond electrical signal may be modified (e.g., by changing one or moreparameters such as pulse frequency, or by interrupting and re-initiatingthe application of the second electrical signal to the cardiac branch ofthe vagus nerve) to control the heart rate below an upper heart ratethreshold and/or body movement exceeds one or more movement thresholds.For example, the frequency or duration of the second electrical signalapplied to the cardiac branch of the vagus nerve may be continuouslymodified based the instantaneous heart rate as monitored during thecourse of a seizure to control what would otherwise be an episode ofictal tachycardia below an upper heart rate threshold. In one exemplaryembodiment, the second electrical signal may be programmed to provide a30-second pulse burst at 30 Hz, with the pulses having a pulse width of0.25 milliseconds and a current of 1.5 milliamps. If, at the end of the30 second burst, the heart rate remains above 120 beats per minute, andis continuing to rise, the burst may be extended to 1 minute instead of30 seconds, the frequency may be increased to 50 Hz, the pulse width maybe increased to 350 milliseconds, or combinations of the foregoing. Instill further embodiments, additional therapies (e.g., oxygen delivery,drug delivery, cooling therapies, etc.) may be provided to the patientif the body data (heart rate, kinetic activity, etc.) indicates that thepatient's seizure is not under control or terminated.

Abnormalities or changes in EKG morphology or rhythm relative to aninterictal morphology or rhythm may also trigger delivery of current tothe heart via the trunks of vagi or its cardiac rami. In otherembodiments, pharmacological agents such as beta-blockers may beautomatically released into a patient's blood stream in response to thedetection of abnormal heart activity during or between seizures.

In one embodiment, the first electrical signal and the second electricalsignal are substantially identical. In another embodiment, the firstelectrical signal may vary from the second electrical signal in terms ofone or more of pulse width, number of pulses, amplitude, frequency,inter-pulse-interval, stimulation on-time, and stimulation off-time,among other parameters and degree, rate or type of charge balancing.

The number of pulses applied to the main trunk or cardiac branch,respectively, before changing the polarity of the first and secondelectrodes need not be one. Thus, two or more pulses may be applied tothe main trunk before applying pulses to the cardiac branch of the vagusnerve. More generally, the first and second signals can be independentof one another and applied according to timing and programmingparameters controlled by the controller 210 and stimulation unit 220.

In one embodiment, one or more pulse bursts of the first electricalsignal are applied to the main trunk of the vagus nerve in response to adetected seizure before applying one or more bursts of the secondelectrical signal to the cardiac branch. In another embodiment, thefirst and second signals are interleaved on a pulse-by-pulse basis underthe control of the controller 210 and stimulation unit 220.

Typically, VNS can be performed with pulse frequency of 20-30 Hz(resulting in a number of pulses per burst of 140-1800, at a burstduration from 7-60 sec). In one embodiment, at least one of the firstelectrical signal and the second electrical signal comprises amicroburst signal. Microburst neurostimulation is discussed by U.S. Ser.No. 11/693,451, filed Mar. 2, 2007 and published as United States patentPublication No. 20070233193, and incorporated herein by reference in itsentirety. In one embodiment, at least one of the first electricalsignal, the second electrical signal, and the third electrical signal ischaracterized by having a number of pulses per microburst from 2 pulsesto about 25 pulses, an interpulse interval of about 2 msec to about 50msec, an interburst period of at least 100 msec, and a microburstduration of less than about 1 sec.

Cranial nerves such as the vagus nerve include different types of nervefibers, such as A-fibers, B-fibers and C-fibers. The different fibertypes propagate action potentials at different velocities. Each nervefiber is directional—that is, endogenous or natural action potentialscan generally propagate action potentials in only one direction(e.g.,afferently to the brain or efferently to the heart and/or viscera). Thatdirection is referred to as the orthodromic direction. Exogenousstimulation (e.g., by electrical pulses) may induce action potentials inboth the orthodromic direction as well as the antidromic direction.Depending upon the desired effects of stimulation (e.g., afferentmodulation of the brain, efferent modulation of the heart, etc.) certainmeasures (e.g., cooling, pressure, etc.) may be taken to blockpropagation in either the efferent or the afferent direction. It isbelieved that the anode may block at least some action potentialstraveling to it from the cathode. For example, referring to FIG. 1, bothafferent and efferent action potentials may be generated in an uppermain trunk of vagus nerve 127-1 by applying a pulse to the nerve usingupper main trunk electrode 125-1 as a cathode. Action potentialsgenerated at upper main trunk electrode 125-1 and traveling toward theheart on cardiac branch 127-2 may be blocked by cardiac branch anode125-2. Action potentials traveling from the upper main trunk 127-1 tothe lower organs in lower main trunk 127-3 may be either blocked (byusing lower main trunk electrode 125-3 as an anode either with orinstead of cardiac branch electrode 125-2) or allowed to travel to thelower organs (by not using electrode structure 125-3 as an electrode).

Action potentials may be generated and allowed to travel to the heart bymaking the electrode 125-2 the cathode. If cardiac branch electrode125-2 is used as a cathode, action potentials will reach the heart inlarge numbers, while action potentials traveling afferently toward thebrain may be blocked in the upper trunk if upper electrode 125-1 is madethe anode.

In a further embodiment of the disclosure, rapid changes in electrodepolarity may be used to generate action potentials to collision blockaction potentials propagating in the opposite direction. To generalize,in some embodiments, the vagus nerve can be selectively stimulated topropagate action potentials either afferently (i.e., to the brain) orefferently (i.e., to the heart and/or lower organs/viscerae).

Turning now to FIG. 2, a block diagram depiction of an implantablemedical device, in accordance with one illustrative embodiment of thepresent disclosure is illustrated. The IMD 200 may be coupled to variouselectrodes 125 and/or 127 via lead(s) 122 (FIGS. 1A, 1C). First andsecond electrical signals used for therapy may be transmitted from theIMD 200 to target areas of the patient's body, specifically to variouselectrodes associated with the leads 122. Stimulation signals from theIMD 200 may be transmitted via the leads 122 to stimulation electrodes(electrodes that apply the therapeutic electrical signal to the targettissue) associated with the electrode assembly 125, e.g., 125-1, 125-2,125-3 (FIG. 1A).

The IMD 200 may comprise a controller 210 capable of controlling variousaspects of the operation of the IMD 200. The controller 210 is capableof receiving internal data and/or external data and controlling thegeneration and delivery of a stimulation signal to target tissues of thepatient's body. For example, the controller 210 may receive manualinstructions from an operator externally, may perform stimulation basedon internal calculations and programming, and may receive and/or processsensor data received from one or more body data sensors such aselectrodes 125-1, 125-2, 125-3, or heart rate sensor 130. The controller210 is capable of affecting substantially all functions of the IMD 200.

The controller 210 may comprise various components, such as a processor215, a memory 217, etc. The processor 215 may comprise one or more microcontrollers, microprocessors, etc., that are capable of executing avariety of software components. The processor may receive, pre-conditionand/or condition sensor signals, and may control operations of othercomponents of the IMD 200, such as stimulation unit 220, seizuredetection module 240, logic unit 250, communication unit, 260, andelectrode polarity reversal unit 280. The memory 217 may comprisevarious memory portions, where a number of types of data (e.g., internaldata, external data instructions, software codes, status data,diagnostic data, etc.) may be stored. The memory 217 may store varioustables or other database content that could be used by the IMD 200 toimplement the override of normal operations. The memory 217 may compriserandom access memory (RAM) dynamic random access memory (DRAM),electrically erasable programmable read-only memory (EEPROM), flashmemory, etc.

The IMD 200 may also comprise a stimulation unit 220. The stimulationunit 220 is capable of generating and delivering a variety of electricalsignal therapy signals to one or more electrodes via leads. Thestimulation unit 220 is capable of delivering a programmed, firstelectrical signal to the leads 122 coupled to the IMD 200. Theelectrical signal may be delivered to the leads 122 by the stimulationunit 220 based upon instructions from the controller 210. Thestimulation unit 220 may comprise various types of circuitry, such asstimulation signal generators, impedance control circuitry to controlthe impedance “seen” by the leads, and other circuitry that receivesinstructions relating to the type of stimulation to be performed.

Signals from sensors (electrodes that are used to sense one or more bodyparameters such as temperature, heart rate, brain activity, etc.) may beprovided to the IMD 200. The body signal data from the sensors may beused by a seizure detection algorithm embedded or processed in seizuredetection module 240 to determine whether or not the patient is havingand/or has had an epileptic seizure. The seizure detection algorithm maycomprise hardware, software, firmware or combinations thereof, and mayoperate under the control of the controller 210. Although not shown,additional signal conditioning and filter elements (e.g., amplifiers,D/A converters, etc., may be used to appropriately condition the signalfor use by the seizure detection module 240. Sensors such as heartsensor 130 and kinetic sensor 140 may be used to detect seizures, alongwith other autonomic, neurologic, or other body data.

The IMD 200 may also comprise an electrode polarity reversal unit 280.The electrode polarity reversal unit 280 is capable of reversing thepolarity of electrodes (125-1, 125-2, 125-3) associated with theelectrode assembly 125. The electrode polarity reversal unit 280 isshown in more detail in FIG. 3. In preferred embodiments, the electrodepolarity reversal unit is capable of reversing electrode polarityrapidly, i.e., in about 10 microseconds or less, and in any event at asufficiently rapid rate to permit electrode polarities to be changedbetween adjacent pulses in a pulsed electrical signal.

The IMD 200 may also comprise a power supply 230. The power supply 230may comprise a battery, voltage regulators, capacitors, etc., to providepower for the operation of the IMD 200, including delivering thestimulation signal. The power supply 230 comprises a power-sourcebattery that in some embodiments may be rechargeable. In otherembodiments, a non-rechargeable battery may be used. The power supply230 provides power for the operation of the IMD 200, includingelectronic operations and the stimulation function. The power supply 230may comprise a lithium/thionyl chloride cell or a lithium/carbonmonofluoride (LiCFx) cell. Other battery types known in the art ofimplantable medical devices may also be used.

The IMD 200 also comprises a communication unit 260 capable offacilitating communications between the IMD 200 and various devices. Inparticular, the communication unit 260 is capable of providingtransmission and reception of electronic signals to and from an externalunit 270. The external unit 270 may be a device that is capable ofprogramming various modules and stimulation parameters of the IMD 200.In one embodiment, the external unit 270 comprises a computer systemthat is capable of executing a data-acquisition program. The externalunit 270 may be controlled by a healthcare provider, such as aphysician, at a base station in, for example, a doctor's office. Theexternal unit 270 may be a computer, preferably a handheld computer orPDA, but may alternatively comprise any other device that is capable ofelectronic communications and programming. The external unit 270 maydownload various parameters and program software into the IMD 200 forprogramming the operation of the implantable device. The external unit270 may also receive and upload various status conditions and other datafrom the IMD 200. The communication unit 260 may be hardware, software,firmware, and/or any combination thereof. Communications between theexternal unit 270 and the communication unit 260 may occur via awireless or other type of communication, illustrated generally by line275 in FIG. 2.

In one embodiment, the communication unit 260 can transmit a log ofstimulation data and/or seizure detection data to the patient, aphysician, or another party.

In one embodiment, a method of treating an epileptic seizure is providedthat involves providing simultaneously both a first electrical signal toa main trunk of a vagus nerve and a second electrical signal to acardiac branch of the vagus nerve. As used herein “simultaneously”refers to the on-time of the first and second signals, and does notrequire that individual pulses of the first signal and the second signalbe simultaneously applied to target tissue. The timing of pulses for thefirst electrical signal and the second electrical signal may bedetermined by controller 210 in conjunction with stimulation unit 220.Where active charge-balancing is used, it may be possible to use theactive charge-balancing phase of pulses of the first electrical signalas the stimulation phase of the second electrical signal by selecting acurrent magnitude of the cathode in the charge-balancing phase(typically a second electrode, which may be the anode of the initialstimulation phase) that is sufficient to generate action potentials innerve fibers of the target tissue. Controller 210 may in someembodiments provide simultaneous delivery of first and second electricalsignals by interleaving pulses for each of the first and secondelectrical signals based upon the programmed timing of pulses for eachsignal and the appropriate polarity of each of first and secondelectrodes 125-1 and 125-2. In some embodiments, additional electrodesmay be used to minimize the induction of action potentials to the heartor the brain provided by the first electrical signal or the secondelectrical signal. This may be accomplished, in one embodiment, by usingan anode located on either the upper main trunk or the cardiac branch toblock impulse conduction to the heart or brain from the cathode, or byproviding dedicated electrode pairs on both the main trunk and cardiacbranches (FIGS. 1D, 1E). When beneficial, steps to avoid collisions ofactions potentials travelling in opposite directions may be implemented,while steps to promote collisions may be taken when clinicallyindicated. In some embodiments, the method further includes sensing acardiac signal and a kinetic signal of the patient, and detecting aseizure event with a seizure detection algorithm.

In one embodiment, a first electrical signal is applied to a main trunkof a vagus nerve and a second electrical signal is simultaneouslyapplied to a cardiac branch of a vagus nerve. A pulse of the firstelectrical signal is generated with the electrical signal generator 110and applied to the main trunk of the vagus nerve using a first electrode(e.g., 125-1, 125-1 a) as a cathode and a second electrode (e.g., 125-1b, 125-3, or 125-2) as an anode. The method includes sensing a cardiacsignal and a kinetic signal of the patient, and detecting a seizureevent with a seizure detection algorithm. A pulse of the secondelectrical signal (having the appropriate pulse width and current) isgenerated and applied (under appropriate timing control by controller110 and stimulation unit 220) to the cardiac branch of the vagus nerveusing a second electrode (e.g., 125-2. 125-2 a) as a cathode and anotherelectrode (e.g., 125-3, 125-1, 125-2 b) as an anode. Another pulse ofthe first electrical signal may thereafter be generated and applied tothe main trunk under timing and parameter control of controller 210 andstimulation unit 220. By appropriate selection of cathodes and anodes,the first and second electrical signals may be interleaved and providedsimultaneously to the main trunk and cardiac branches of the vagusnerve. In some embodiments, the number of electrodes may be minimized byprovided a polarity reversal unit that may rapidly change the polarityof particular electrodes to allow their use in delivering both the firstand second signals.

The IMD 200 is capable of delivering stimulation that can be contingent,periodic, random, coded, and/or patterned. The stimulation signals maycomprise an electrical stimulation frequency of approximately 0.1 to10,000 Hz. The stimulation signals may comprise a pulse width in therange of approximately 1-2000 micro-seconds. The stimulation signals maycomprise current amplitude in the range of approximately 0.1 mA to 10mA. Appropriate precautions may be taken to avoid delivering injuriouscurrent densities to target neural tissues, e.g., by selecting current,voltage, frequency, pulse width, on-time and off-time parameters tomaintain current density below thresholds for damaging tissues.

The IMD 200 may also comprise a magnetic field detection unit 290. Themagnetic field detection unit 290 is capable of detecting magneticand/or electromagnetic fields of a predetermined magnitude. Whether themagnetic field results from a magnet placed proximate to the IMD 200, orwhether it results from a substantial magnetic field encompassing anarea, the magnetic field detection unit 290 is capable of informing theIMD of the existence of a magnetic field. The changeable electrodepolarity stimulation described herein may be activated, deactivated, oralternatively activated or deactivated using a magnetic input.

The magnetic field detection unit 290 may comprise various sensors, suchas a Reed Switch circuitry, a Hall Effect sensor circuitry, and/or thelike. The magnetic field detection unit 290 may also comprise variousregisters and/or data transceiver circuits that are capable of sendingsignals that are indicative of various magnetic fields, the time periodof such fields, etc. In this manner, the magnetic field detection unit290 is capable of detecting whether the detected magnetic field relatesto an input to implement a particular first or second electrical signal(or both) for application to the main trunk of cardiac branches,respectively, of the vagus nerve.

One or more of the blocks illustrated in the block diagram of the IMD200 in FIG. 2, may comprise hardware units, software units, firmwareunits, or any combination thereof. Additionally, one or more blocksillustrated in FIG. 2 may be combined with other blocks, which mayrepresent circuit hardware units, software algorithms, etc.Additionally, one or more of the circuitry and/or software unitsassociated with the various blocks illustrated in FIG. 2 may be combinedinto a programmable device, such as a field programmable gate array, anASIC device, etc.

FIG. 3 shows in greater detail an electrode polarity reversal unit 280(FIG. 2) in one embodiment. The electrode polarity reversal unit 280comprises an electrode configuration switching unit 340, which includesa switching controller 345. The switching controller 345 transmitssignals to one or more switches, generically, n switches 330(1), 330(2),. . . 330(n) which effect the switching of the configuration of two ormore electrodes, generically, n electrodes 125(1), 125(2), . . . 125(n).Although FIG. 3 shows equal numbers of switches 330 and electrodes 125,persons of skill in the art having the benefit of the present disclosurewill understand that the number of switches 330 and their connectionswith the various electrodes 125 can be varied as a matter of routineoptimization. A switching timing unit 333 can signal to the electrodeconfiguration switching unit 340 that a desired time for switching theelectrode configuration has been reached.

Instructions for implementing two or more stimulation regimens, whichmay include at least one open-loop electrical signal and at least oneclosed-loop electrical signal, may be stored in the IMD 200. Thesestimulation signals may include data relating to the type of stimulationsignal to be implemented. In one embodiment, an open-loop signal may beapplied to generate action potentials for modulating the brain of thepatient, and a closed-loop signal may be applied to generate eitheraction potentials for slowing the heart rate of the patient, or bothaction potentials to modulate the brain of the patient as well as actionpotentials for slowing the heart rate of the patient. In someembodiments, the open-loop and closed-loop signals may be provided todifferent target portions of a vagus nerve of the patient by switchingthe polarity of two or more electrodes using an electrode polarityreversal unit as described in FIG. 3 above. In alternative embodiments,additional electrodes may be provided to generate each of the open-loopand closed-loop signals without electrode switching.

In one embodiment, a first open-loop mode of stimulation may be used toprovide an electrical signal to a vagus nerve using a first electrode asa cathode on a main trunk (e.g., 127-1 or 127-3 using electrodes 125-1or 125-3, respectively) of a vagus nerve, and a second electrode as ananode on either a main trunk (e.g., electrode 125-3, when electrode125-1 is used as a cathode) or cardiac branch (e.g., electrode 125-2) ofa vagus nerve. The first open-loop signal may include a programmedon-time and off-time during which electrical pulses are applied (theon-time) and not-applied (the off-time) in a repeating sequence to thevagus nerve.

A second, closed-loop signal may be provided in response to a detectedevent (such as an epileptic seizure, particularly when accompanied by anincrease in the patient's heart rate) using a different electrodeconfiguration than the first, open-loop signal. In one embodiment, thesecond, closed-loop signal is applied to a cardiac branch using thesecond electrode 125-2 as a cathode and the first electrode on the maintrunk (e.g., 125-1 or 125-3) as an anode. The second, closed-loop signalmay involve generating efferent action potentials on the cardiac branchof the vagus nerve to slow the heart rate. In some embodiments, thefirst, open-loop signal may be interrupted/suspended in response to thedetected event, and only the second, closed-loop signal is applied tothe nerve. In other embodiments, the first, open loop signal may not beinterrupted when the event is detected, and both the first, open-loopsignal and the second, closed-loop signal are applied to the vagusnerve. In another embodiment, a third, closed-loop signal may also beprovided in response to the detected event. The third, closed-loopsignal may involve an electrical signal using the same electrodeconfiguration as the first, open-loop electrical signal, but may providea different electrical signal to the main trunk of the vagus nerve thaneither the first, open-loop signal or the second, closed-loop signal.The first, open-loop signal may be interrupted, terminated or suspendedin response to the detected event, and the third, closed-loop signal maybe applied to the nerve either alone or with the second, closed-loopsignal. In some embodiments, both the second and third closed-loopsignals may be provided in response to a detected epileptic seizure byrapidly changing the polarity of the first (125-1) and second (125-2)electrodes from cathode to anode and back, as pulses are provided aspart of the second and third electrical signals, respectively. In oneembodiment, the third electrical signal may involve modulating the brainby using a main trunk electrode (e.g., upper main trunk electrode 125-1)as a cathode and another electrode (e.g., cardiac branch electrode 125-2or lower main trunk electrode 125-3) as an anode. The third electricalsignal may comprise, for example, a signal that is similar to the firstelectrical signal but which provides a higher electrical current thanthe first electrical signal, and for a longer duration than the firstsignal or for a duration that is adaptively determined based upon asensed body signal (in contrast, for example, to a fixed duration of thefirst electrical signal determined by a programmed on-time). By rapidlychanging polarity of the electrodes, pulses for each of the second andthird electrical signals may be provided such that the second and thirdsignals are provided simultaneously to the cardiac branch and main trunkof the vagus nerve. In other embodiments, the first, second and thirdelectrical signals may be provided sequentially rather thansimultaneously.

some embodiments, one or more of the first, second and third electricalsignals may comprise a microburst signal, as described more fully inU.S. patent application Ser. No. 11/693,421, 11/693,451, and Ser. No.11/693,499, each filed Mar. 29, 2007 and each hereby incorporated byreference herein in their entirety.

In one embodiment, each of a plurality of stimulation regimens mayrespectively relate to a particular disorder, or to particular eventscharacterizing the disorder. For example, different electrical signalsmay be provided to one or both of the main trunk and cardiac branches ofthe vagus nerve depending upon what effects accompany the seizure. In aparticular embodiment, a first open-loop signal may be provided to thepatient in the absence of a seizure detection, while a second,closed-loop signal may be provided when a seizure is detected based on afirst type of body movement of the patient as detected by, e.g., anaccelerometer, a third, closed-loop signal may be provided when theseizure is characterized by a second type of body movement, a fourth,closed-loop signal may be provided when the seizure is characterized byan increase in heart rate, a fifth, closed-loop signal may be providedwhen the seizure is characterized by a decrease in heart rate, and soon. More generally, stimulation of particular branches or main trunktargets of a vagus nerve may be provided based upon different bodysignals of the patient. In some embodiments, additional therapies may beprovided based on different events that accompany the seizure, e.g.,stimulation of a trigeminal nerve or providing a drug therapy to thepatient through a drug pump. In one embodiment, different regimensrelating to the same disorder may be implemented to accommodateimprovements or regressions in the patient's present condition relativeto his or her condition at previous times. By providing flexibility inelectrode configurations nearly instantaneously, the present disclosuregreatly expands the range of adjustments that may be made to respond tochanges in the patient's underlying medical condition.

The switching controller 345 may be a processor that is capable ofreceiving data relating to the stimulation regimens. In an alternativeembodiment, the switching controller may be a software or a firmwaremodule. Based upon the particulars of the stimulation regimens, theswitching timing unit 333 may provide timing data to the switchingcontroller 345. The first through nth switches 330(1-n) may beelectrical devices, electro-mechanical devices, and/or solid statedevices (e.g., transistors).

FIG. 4 shows one embodiment of a method of treating a patient havingepilepsy according to the present disclosure. In this embodiment, afirst electrode is coupled to a main trunk of a vagus nerve of thepatient (410) and a second electrode is coupled to a cardiac branch ofthe vagus nerve (420). An electrical signal generator is coupled to thefirst and second electrodes (430).

The method further involves receiving at least one body data stream ofthe patient (440). The data may be sensed by a sensor such as heart ratesensor 130 (FIG. 1A) or a sensor that is an integral part of, or coupledto, an IMD 200 (FIG. 2) such as electrical pulse generator 110 (FIG.1A), and the IMD may also receive the data from the sensor. The at leastone body data stream is then analyzed using a seizure detectionalgorithm (450), and the seizure detection algorithm determines whetheror not the patient is having and/or has had an epileptic seizure (460).

If the algorithm indicates that the patient is not having and/or has nothad an epileptic seizure, the method comprises applying a firstelectrical signal from the electrical signal generator to the main trunkof a vagus nerve using the first electrode as a cathode (470). In oneembodiment, applying the first electrical signal comprises continuing toapply a programmed, open-loop electrical signal periodically to the maintrunk of the vagus nerve according a programmed on-time and off-time.

If the algorithm indicates that the patient is having and/or has had anepileptic seizure, the method comprises applying a second electricalsignal from the electrical signal generator to the cardiac branch of thevagus nerve using the second electrode as a cathode (480). Dependingupon which electrical signal (first or second) is applied, the methodmay involve changing the polarity of one or both of the first electrodeand the second electrode. In one embodiment, the method may comprisesuspending the first electrical and applying the second electricalsignal. In one embodiment, the method comprises continuing to receive atleast one body data stream of the patient at 440 after determiningwhether or not the patient is having and/or has had an epilepticseizure.

In an alternative embodiment, if the seizure detection algorithmindicates that the patient is having and/or has had an epilepticseizure, both the first electrical signal and the second electricalsignal are applied to the main trunk and cardiac branches of a vagusnerve of the patient, respectively, at step 480. In a specificimplementation of the alternative embodiment, pulses of the first andsecond electrical signal are applied to the main trunk and cardiacbranch of the vagus nerve under the control of controller 210 by rapidlychanging the polarity of the first and second electrodes using theelectrode polarity reversal unit 280 to apply the first electricalsignal to the main trunk using the first electrode as a cathode and thesecond electrode as an anode, changing the polarity of the first andsecond electrodes, and applying the second electrical signal to thecardiac branch using the second electrode as a cathode and the firstelectrode as an anode. Additional pulses for each signal may besimilarly applied by rapidly changing the polarity of the electrodes.

In some embodiments, the first electrical signal and the secondelectrical signal are applied unilaterally, i.e., to a vagal main trunkand a cardiac branch on the same side of the body. In other embodiments,the first and second electrical signals are applied bilaterally, i.e.,the second electrical signal is applied to a cardiac branch on theopposite side of the body from the main vagal trunk to which the firstelectrical signal is applied. In one embodiment, the first electricalsignal is applied to a left main trunk to minimize cardiac effects ofthe first electrical signal, and the second electrical signal is appliedto a right cardiac branch, which modulates the sinoatrial node of theheart to maximize cardiac effects of the second electrical signal.

In alternative embodiments, both the first electrode and the secondelectrode may be coupled to a cardiac branch of a vagus nerve, with thefirst electrode (e.g., anode) being proximal to the brain relative tothe second electrode, and the second electrode (e.g., cathode) beingproximal to the heart relative to the first electrode.

FIG. 5 is a flow diagram of another method of treating a patient havingepilepsy according to the present disclosure. A sensor is used to sensea cardiac signal and a kinetic signal of the patient (540). In aparticular embodiment, the cardiac sensor may comprise an electrode pairfor sensing an ECG (electrocardiogram) or heart beat signal, and thekinetic signal may comprise a triaxial accelerometer to detect motion ofat least a portion of the patient's body. The method further comprisesanalyzing at least one of the cardiac signal and the kinetic signalusing seizure detection algorithm (550), and the output of the algorithmis used to determine whether at least one of the cardiac signal and thekinetic signal indicate that the patient is having and/or has had anepileptic seizure (560).

If the patient is not having and/or has not had an epileptic seizure,the method comprises applying a first electrical signal to a main trunkof a vagus nerve of the patient using a first electrode, coupled to themain trunk, as a cathode (580). In one embodiment, the first electricalsignal is an open-loop electrical signal having an on-time and off-time.

If the patient is having and/or has had an epileptic seizure, adetermination is made whether the seizure is characterized by anincrease in the patient's heart rate (570). If the seizure is notcharacterized by an increase in the patient's heart rate, the methodcomprises applying the first electrical signal to the main trunk of avagus nerve using the first electrode as a cathode (580). In oneembodiment, the cathode comprises an upper main trunk electrode 125-1and the anode is selected from a cardiac branch electrode 125-2 and alower main trunk electrode 125-3. Conversely, if the seizure ischaracterized by an increase in the patient's heart rate, the methodcomprises applying a second electrical signal to a cardiac branch of avagus nerve of the patient using a second electrode, coupled to thecardiac branch, as a cathode (590). The anode is an upper main trunkelectrode 125-1 or a lower main trunk electrode 125-3. In oneembodiment, the method may comprise suspending the first electrical andapplying the second electrical signal.

The method then continues the sensing of the cardiac and kinetic signalsof the patient (540) and resumes the method as outlined in FIG. 5.

FIG. 6 is a flow diagram of a further method of treating a patienthaving epilepsy according to the present disclosure. The method includesapplying a first, open-loop electrical signal to a main trunk of a vagusnerve (610). The open-loop signal is characterized by an off-time inwhich electrical pulses are applied to the nerve, and an off-time inwhich electrical pulses are not applied to the nerve.

A sensor is used to sense at least one body signal of the patient (620),and a determination is made whether the at least one body signalindicates that the patient is having and/or has had an epileptic seizure(630). If the patient is not having and/or has not had a seizure, themethod continues applying the first, open-loop electrical signal to amain trunk of a vagus nerve (610). If the patient is having and/or hashad an epileptic seizure, a determination is made whether the seizure ischaracterized by an increase in the patient's heart rate (640). In oneembodiment, the increase in heart rate is measured from a baseline heartrate existing prior to the seizure, e.g., a median heart rate for aprior period such as the 300 beats prior to the detection of the seizureevent, or the 5 minutes prior to the detection of the seizure.

If the seizure is not characterized by an increase in the patient'sheart rate, the method comprises applying a second, closed-loopelectrical signal to the main trunk of the vagus nerve 650). In oneembodiment, the second, closed-loop electrical signal is the same signalas the open-loop electrical signal, except that the second signal (asdefined, e.g., by a current intensity, a pulse frequency, a pulse widthand an on-time) is applied at a time different from the programmedtiming of the first electrical signal. For example, if the firstelectrical signal comprises an on-time of 30 seconds and an off-time of5 minutes, but a seizure is detected 1 minute after the end of aprogrammed on-time, the second electrical signal may comprise applying a30 second pulse burst at the same current intensity, frequency, andpulse width as the first signal, but four minutes earlier than wouldhave occurred absent the detected seizure. In another embodiment, thesecond, closed-loop electrical signal is a different signal than thefirst, open-loop electrical signal, and the method may also comprisesuspending the first electrical before applying the second electricalsignal. For example, the second, closed-loop electrical signal maycomprise a higher current intensity, frequency, pulse width and/oron-time than the first, open-loop electrical signal, and may notcomprise an off-time (e.g., the second electrical signal may be appliedfor a predetermined duration independent of the on-time of the first,open-loop electrical signal, such as a fixed duration of 1 minute, ormay continue for as long as the body signal indicates the presence ofthe seizure event).

Returning to FIG. 6, if the seizure is characterized by an increase inthe patient's heart rate, the method comprises applying a third,closed-loop electrical signal to a cardiac branch of a vagus nerve toreduce the patient's heart rate (660). The method may comprisesuspending the first electrical as well as applying the third,closed-loop electrical signal. In one embodiment of the disclosure, eachof the first, open-loop electrical signal, the second, closed-loopelectrical signal, and the third, closed-loop electrical signal areapplied unilaterally (i.e., to vagus nerve structures on the same sideof the body) to the main trunk and cardiac branch of the vagus nerve.For example, the first, open-loop electrical signal and the second,closed-loop electrical signal may be applied to a left main trunk of thepatient's cervical vagus nerve, and the third, closed-loop electricalsignal may be applied to the left cardiac branch of the vagus nerve.Similarly, the first, second and third electrical signals may all beapplied to the right vagus nerve of the patient. In alternativeembodiments, one or more of the first, second and third electricalsignals may be applied bilaterally, i.e., one of the first, second andthird electrical signals is applied to a vagal structure on the oppositeside of the body from the other two signals. For example, in aparticular embodiment the first, open-loop signal and the second,closed-loop signal may be applied to a left main trunk of the patient'scervical vagus nerve, and the third, closed-loop electrical signal maybe applied to a right cardiac branch of the patient's vagus nerve.Because the right cardiac branch modulates the sinoatrial node of thepatient's heart, which is the heart's “natural pacemaker,” the thirdelectrical signal may have more pronounced effect in reducing thepatient's heart rate if applied to the right cardiac branch.

After applying one of the second (650) and third (660) electricalsignals to a vagus nerve of the patient, the method then continuessensing at least one body signal of the patient (620) and resumes themethod as outlined in FIG. 6.

In the methods depicted in FIGS. 4-6, one or more of the parametersdefining the first, second, and third electrical signals (e.g., numberof pulses, pulse frequency, pulse width, On time, Off time, interpulseinterval, number of pulses per burst, or interburst interval, amongothers) can be changed by a healthcare provided using a programmer 150.

FIG. 7 is a flow diagram of a method of treating patients havingseizures accompanied by increased heart rate. In one embodiment,tachycardia is defined as a neurogenic increase in heart rate, that is,an elevation in heart rate that occurs in the absence of motor activityor that if associated with motor activity, the magnitude of the increasein heart rate is larger than that caused by motor activity alone. In oneembodiment, a body signal is acquired (710). The body signal maycomprise one or more body signals that may be altered, changed orinfluenced by an epileptic seizure. As non-limiting examples, the bodysignal may comprise one or more of a cardiac signal such as heart rate,heart rate variability, or EKG complex morphology, a kinetic signal suchas an accelerometer signal, a postural signal or body position signal),blood pressure, blood oxygen concentration, skin resistivity orconductivity, pupil dilation, eye movement, EEG, reaction time or otherbody signals. The body signal may be a real-time signal or a storedsignal for delayed or later analysis. It may be acquired, for example,from a sensor element (e.g., coupled to a processor), from a storagedevice in which the signal data is stored.

The method further comprises determining whether or not the patient ishaving and/or has had a seizure accompanied by an increase in heart rate(720). In one embodiment, the method comprises a seizure detectionalgorithm that analyzes the acquired body signal data and determineswhether or not a seizure has occurred. In a particular embodiment, themethod comprises an algorithm that analyzes one or more of a cardiacsignal, a kinetic signal, a cognitive signal, blood pressure, bloodoxygen concentration, skin resistivity or conductivity, pupil dilation,and eye movement to identify changes in the one or more signals thatindicate a seizure has occurred. The method may comprise an outputsignal or data flag that may be asserted or set when the detectionalgorithm determines from the body signal(s) that the patient is havingand/or has had a seizure.

The method also comprises determining (720) whether or not the seizureis accompanied by an increase in heart rate. In one embodiment, the bodydata signal comprises a heart beat signal that may be analyzed todetermine heart rate. In some embodiments, the heart beat signal may beused by the seizure detection algorithm to determine whether a seizurehas occurred, while in other embodiments seizures are not detected usingheart rate. Regardless of how the seizure is detected, however, themethod of FIG. 7 comprises determining whether a detected seizure eventis accompanied by an increase in heart rate. The increase may bedetermined in a variety of ways, such as by an increase in aninstantaneous heart rate above a reference heart rate (which may be apredetermined interictal value such as 72 beats per minute (bpm), or areal-time measure of central tendency for a time window, such as a 5minute median or moving average heart rate). Additional details aboutidentifying increases in heart rate in the context of epileptic seizuresare provided in U.S. Pat. Nos. 5,928,272, 6,341,236, 6,587,727,6,671,556, 6,961,618, 6,920,357, 7,457,665, as well as U.S. patentapplication Ser. Nos. 12/770,562, 12/771,727, 12/771,783, 12/884,051,12/886,419, 12/896,525, 13/098,262, and 13/288,886, each of which ishereby incorporated by reference in its entirety herein.

If the body data signal does not indicate that the patient is havingand/or has had a seizure accompanied by tachycardia, the methodcomprises applying a first electrical signal to a left vagus nerve. Ifthe body signal does indicate that the patient has experienced a seizureaccompanied by tachycardia, the method comprises applying a secondelectrical signal to a right vagus nerve.

Without being bound by theory, it is believed that stimulation of theright vagus nerve, which enervates the right sinoatrial nerve thatfunctions as the heart's natural pacemaker, will have a more prominenteffect in slowing the heart rate than stimulation of the left vagusnerve. The present disclosure takes advantage of this electricalasymmetry of the left and right vagus nerves to minimize the effect ofVNS on heart rate except where there is a need for acute intervention toslow the heart rate, i.e., when the patient has experienced andepileptic seizure, and the seizure is accompanied by an increase inheart rate. This may result in, for example, stimulation of the leftvagus nerve either when there is no seizure (such as when an open-loopstimulation program off-time has elapsed and the program initiatesstimulation in accordance with a programmed signal on-time), or whenthere is a detected seizure event that is not accompanied by an increasein heart rate (such as absence seizures); and stimulation of the rightvagus nerve when there is a detected seizure event accompanied by aheart rate increase. In one embodiment, a programmed, open-loopelectrical signal is applied to the left vagus nerve except when analgorithm analyzing the acquired body signal detects a seizureaccompanied by a heart rate increase. In response to such a detection, aclosed-loop electrical signal is applied to the right vagus nerve toslow the patient's (increased) heart rate. In some embodiments, theresponse to detecting a seizure accompanied by a heart rate increase mayalso include interrupting the application of the programmed-open-loopelectrical signal to the left vagus nerve. The interrupted open-loopstimulation of the left vagus nerve may be resumed either when theseizure ends or the heart rate returns to a desired, lower heart rate.

In an additional embodiment of the disclosure, electrode pairs may beapplied to each of the left and right vagus nerves of the patient, andused depending upon whether or not seizures accompanied by cardiacchanges such as tachycardia are detected.

FIG. 8 is a flowchart depiction of a method of treating patients havingseizures accompanied by a relative or absolute decrease in heart rate(i.e., a bradycardia episode). Epileptic seizures originating fromcertain brain regions may trigger decreases in heart rate of a magnitudesufficient to cause loss of consciousness and of postural tone (i.e.,syncope). In some subjects the cerebral ischemia associated with thebradycardia may in turn lead to convulsions (i.e., convulsive syncope).If bradycardia-inducing seizures are not controllable by medications,the current treatment is implantation of a demand cardiac pacemaker. Inone embodiment of the present disclosure, ictal bradycardia may betreated by preventing vagal nerve impulses from reaching the heart,either by preventing impulses traveling through all fiber typescontained in the trunk of the nerve or in one of its branches, or byonly blocking impulses within a certain fiber type. In anotherembodiment, the degree of the nerve impulse blocking within a vagusnerve may be determined based upon the magnitude of bradycardia (e.g.,the larger the bradycardia change from the pre-existing baseline heartrate, the larger the magnitude of the block) so as to preventtachycardia from occurring.

In one embodiment, a body signal is acquired (810). The body signal maycomprise one or more body signals that may be altered, changed orinfluenced by an epileptic seizure. Changes in the body signal may beused to detect the onset or impending onset of seizures. As noted withreference to FIG. 7, the body signal may comprise one or more measurederived from a cardiac signal (e.g., heart rate, heart rate variability,change in EKG morphology), a kinetic signal (e.g., an accelerometer,force of muscle contraction, posture or body position signal), bloodpressure, blood oxygen concentration, skin resistivity/conductivity,pupil dilation, eye movement, or other body signals. The body signal maybe a real-time signal, a near-real-time signal, or a non-real-timesignal, although in preferred embodiments, the signal is a real-timesignal or a near-real-time signal. The signal may be acquired from asensor element (e.g., coupled to a processor) or from a storage device.

Referring again to FIG. 8, the method further comprises determiningwhether or not the patient is having and/or has had a seizure that isaccompanied by a decrease in heart rate (820). In one embodiment, themethod comprises using a seizure detection algorithm using one or moreof a cardiac, kinetic, neurologic, endocrine, metabolic or tissue stressmarker to detect seizures, and to determine if the seizure is associatedwith a decrease in heart rate. In a particular embodiment, analgorithm—which may comprise software and/or firmware running in aprocessor in a medical device—analyzes one or more of a cardiac signal,a kinetic signal, blood pressure, blood oxygen concentration, skinresistivity or conductivity, pupil dilation, and eye movement toidentify changes in the one or more signals that indicate the occurrenceof an epileptic seizure. Such changes may be identified by determiningone or more indices from the foregoing signals, such as a cardiac index(e.g., a heart rate), a kinetic index (e.g., a kinetic level or motiontype, a magnitude of an acceleration or force, or other indices that maybe calculated from an accelerometer signal). The method may includeproviding an output signal or setting a data flag when the detectionalgorithm determines from the body signal(s) that the patient is havingand/or has had a seizure. In a preferred embodiment, the seizuredetection occurs in real time and the output signal or data flag is setimmediately upon detection of the seizure.

Once it is determined that the patient is having and/or has had aseizure, the method also comprises determining if the seizure isaccompanied by a decrease in heart rate. In one embodiment, the acquiredbody data signal (810) comprises a heart beat signal that may beanalyzed to determine heart rate. In some embodiments, the acquiredheart beat signal may be used by the seizure detection algorithm todetermine whether a seizure has occurred, while in other embodimentsseizures are determined without regard to the patient's heart rate.Regardless of how the seizure is determined, the method of FIG. 8comprises determining whether a detected seizure event is accompanied bya decrease in heart rate (820). The decrease in heart rate may bedetermined in a variety of ways, such as by a decrease in aninstantaneous heart rate below a reference heart rate value (which maybe a predetermined interictal value such as 72 beats per minute (bpm),or a real-time measure of central tendency for a time window ornumber-of-beats window (e.g., a 5 minute median or moving average heartrate, or a media heart rate for a window selected from 3-300 beats suchas a 5, 10, or 300 beat window)). Additional details about identifyingdecreases in heart rate in the context of epileptic seizures areprovided in U.S. patent application Ser. Nos. 12/770,562, 12/771,727,12/771,783, 12/884,051, 12/886,419, 13/091,033, each of which is herebyincorporated by reference in its entirety herein.

In one embodiment, if the acquired body data signal does not indicatethat the patient is having and/or has had a seizure accompanied by a HRdecrease, the method comprises applying a first electrical signal to avagus nerve (840), wherein the first electrical signal is sufficient togenerate exogenous action potentials in fibers of the vagus nerve. Thesecond electrical signal is a therapeutic electrical signal to treat theseizure. It may be applied to either the left or right vagus nerves, orboth. The first electrical signal may be a signal defined by, amongother parameters, an on-time during which electrical pulses are appliedto the nerve, and an off-time during which no pulses are applied to thenerve. In some embodiments, the on-time may be determined by theduration and intensity of the change in heart rate, while in otherembodiments it may be pre-programmed. Cathode(s) and anode(s) may beplaced on the nerve trunks or branches to maximize flow of exogenouslygenerated nerve impulses in a caudal direction (for control of heartrate changes) and a cephalic direction for seizure treatment.

If the body signal indicates that the patient is having and/or has had aseizure accompanied by a decrease in heart rate, the method comprisesapplying an action to decrease vagal/parasympathetic tone. In oneembodiment, the method comprises blocking the passage of impulsesthrough at least one of a vagus nerve trunk or branch. This may beaccomplished by applying one or more of a second electrical signal(e.g., a high frequency electrical signal), a thermal signal (e.g.,cooling), a chemical signal (e.g., applying a local anesthetic), and/ora mechanical signal (e.g., applying pressure or a vibration) to a vagusnerve of the patient (830). In another embodiment, the method comprisesdelivering at least one of an anti-cholinergic drug or asympatho-mimetic drug.

As used herein, blocking vagus nerve activity means blocking intrinsicor native vagal activity (i.e., blocking action potentials notartificially or exogenously induced by an electrical signal generated bya device). The blocking signal may block the conduction of actionpotentials in all or at least some portion or fraction of the axons of avagus nerve. In general, such blocking signals are incapable of inducingexogenous action potentials in the axons of the vagus nerve. In oneembodiment, the blocking signal may comprise a high frequency, pulsedelectrical signal, the pulse frequency being sufficient to inhibitpropagation of at least some action potentials in vagus nerve fibers.The electrical signal may comprise a signal in excess of 300Hz, or otherfrequency, so long as the frequency and other stimulation signalparameters (such as pulse width and pulse current or voltage) provide asignal capable of inhibiting some or all of the action potentialspropagating along fibers of the vagus nerve. In alternative embodiments,the electrical signal may comprise generating unidirectional actionpotentials for collision blocking of endogenous action potentials.

High frequency vagus nerve stimulation (or other blocking signals suchas collision blocking) may inhibit pathological vagus nerve activityassociated with the seizure that may be acting to slow the patient'sheart rate. By providing such stimulation only when the patientexperiences a seizure accompanied by a reduced heart rate (e.g.,bradycardia), a therapy may be provided that acts to maintain thepatient's heart rate when the patient experiences a seizure involvingexcessive vagal activity—and consequent undesired slowing of—the heart.In one embodiment, the blocking electrical signal (830) is provided to aright vagus nerve. Without being bound by theory, because the rightvagus nerve innervates the right sinoatrial node that functions as theheart's natural pacemaker, it is believed that right-side VNS will havea more significant effect upon the heart rate than stimulation of theleft vagus nerve. In alternative embodiments, the blocking signal may beapplied to the left vagus nerve, to both the right and left vagusnerves, or to one or both of the left and right cardiac branches of thevagus nerves.

In one embodiment, the method comprises applying a first electricalsignal that may be a conventional vagus nerve stimulation signal definedby a plurality of parameters (e.g., a pulse width, a current magnitude,a pulse frequency, an on-time and an off-time). A seizure detectionalgorithm (e.g., using one or more of a cardiac, kinetic, metabolic,EEG, or other body signal) may be used to detect seizures, and thepatient's heart rate may be determined proximate the seizure detectionto determine if the seizure is accompanied by a decrease in thepatient's heart rate. If the seizure is accompanied by a slowing of thepatient's heart rate, the first electrical signal may be suspended, anda second electrical signal may be applied to slow the patient's heartrate. The method may further include sensing the patient's heart rateduring or after application of the second electrical signal. In oneembodiment, the second electrical signal may be modified (e.g., bychanging current magnitude, pulse width, or pulse frequency), orsuspended (and possibly resumed) to maintain the patient's heart ratebetween an upper heart rate threshold and a lower heart rate threshold.In some embodiments, the upper and lower heart rate thresholds may bedynamically set (e.g., as no more than 5 bpm above or below the baselineHR prior to the seizure detection).

FIG. 9 is a flow diagram of a method of treating a patient with epilepsyby providing closed-loop vagus nerve intervention (e.g., stimulation orblockage of impulse conduction) to maintain the patient's heart ratewithin a range that is both safe and also commensurate with the activitytype or level and state of the patient (e.g., as determined from akinetic signal from a sensing element such as a triaxial accelerometeror by measuring oxygen consumption). In one embodiment, the methodcomprises providing vagus nerve stimulation in response to determiningthat a heart rate is incommensurate with the kinetic signal of thepatient, to restore cardiac function to a rate that is commensurate withthe patient's kinetic signal. In one embodiment, the stimulation maycomprise stimulating a right vagus nerve to slow the patient's heartrate to a level that is safe and/or commensurate with activity level. Inanother embodiment, the stimulation may comprise providing a blockingsignal to increase a slow heart rate to a rate that is safe and/orcommensurate with the activity level. Pharmacologic compounds (e.g.,drugs) with sympathetic or parasympathetic effects (e.g., enhancing orblocking sympathetic or parasympathetic activity) may be used to restoreheart rate to a rate commensurate with kinetic activity of the patientin still other embodiments. In one embodiment, the method involvesdetermining a heart rate and one or more kinetic or metabolic (e.g.,oxygen consumption) indices for the patient (910). Heart rate may bedetermined from an acquired cardiac signal (e.g., from a sensor orstored data). Kinetic and/or metabolic indices may likewise bedetermined from a kinetic sensor (e.g., an accelerometer, a positionalsensor, a GPS device coupled to a clock, or a postural sensor), ametabolic sensor, or from stored data. Sensor data may be subjected toone or more operations such as amplifying, filtering, A/D conversion,and/or other pre-processing and processing operations to enabledetermination of heart rate (and in some embodiments other cardiacindices such as heart rate variability) and kinetic indices.

The activity level of the patient may be determined from multiplekinetic indications such as an activity level, a type of activity, aposture, a body position, a trunk or limb acceleration or force, or aduration of one of the foregoing, and may be adapted or modified as afunction of age, gender, body mass index, fitness level or time of dayor other indices of the patient's condition or environment. For example,the kinetic signal may be processed to provide indices that indicatemoderate ambulatory motion for an upright patient, vigorous physicalexercise (in which the patient may be upright as in running or in aprone position as in some calisthenics exercises), a fall (e.g.,associated with a seizure), reclining, resting or sleeping, among otheractivity levels and kinetic states.

The one or more kinetic indices may then be used to determine (e.g., byretrieving stored data from a lookup table or by calculation using analgorithm) one or more heart rate ranges or values that would becommensurate with the kinetic activity and/or kinetic state, duration,time of day, etc. associated with the indices. In some embodiments,heart rate ranges may be established for particular levels or types ofactivity (e.g., running, walking), that may be adaptively adjusteddepending upon various factors such as the duration of the activity, thepatient's fitness level, the time of day, a level of fatigue, anenvironmental temperature, etc. A commensurate heart rate is one that iswithin expected ranges or values for the person's effort, and forfactors inherent to the patient and the environment.

Returning to FIG. 9, the determined heart rate may be compared to therange(s)/value(s) identified as commensurate with the kinetic indices(920) at a given time point. If the actual heart rate of the patient iswithin the expected/commensurate range or value associated with thekinetic or metabolic indices at the time point, or is within a specifiedproximity of a particular range or value, no action may be taken, andthe method may involve continuing to analyze the patient's cardiac andkinetic signals or metabolic signals. On the other hand, if the heartrate is outside the expected value or range of values for the kinetic ormetabolic indices for that time point, then the heart rate is notcommensurate with the kinetic signal of the patient, and a therapy maybe provided to the patient by applying one of an electrical, thermal,mechanical or chemical signal to a vagus nerve of the patient (930) oradministering to the patient (e.g., intravenously, through mucosae) adrug with cholinergic or anti-cholinergic or adrenergic actions,depending on the case or situation. In one embodiment, the method maycomprise applying the signal to a main trunk of a vagus nerve of thepatient, and in another embodiment, the signal may be applied to acardiac branch of a vagus nerve.

In one embodiment, the heart rate of the patient may be higher than avalue commensurate with the activity level or kinetic indices of thepatient. In this case, the patient is having relative tachycardia. Wherethis is the case, as previously noted, vagus nerve stimulation may beapplied to one or more of a right cardiac branch, left cardiac branch,or right main trunk of the patient's vagus nerve to reduce the patient'sheart rate to a rate that is commensurate with the activity level.Embodiments of the disclosure may be used to treat epileptic seizuresassociated with tachycardia, and other medical conditions associatedwith tachycardia given the patient's activity level. Therapies (e.g.,electrical, chemical, mechanical, thermal) delivered to a patient viathe vagus nerves may be employed for tachyarrythmias, angina pectoris orpain in regions innervated by a vagus nerve.

In another embodiment, the patient's heart rate may be lower than avalue commensurate with the patient's activity level or kinetic indices,that is, the patient is having relative or absolute bradycardia. Highfrequency (>>300 Hz) electrical pulses may be applied to the left orright vagus nerves (e.g., a main trunk of the right and/or left vagusnerves or to their cardiac branches) to block propagation oftransmission of nerve impulses through their fibers. High-frequency VNSmay be applied to block impulses traveling to the heart to abateneurogenic, cardiogenic or iatrogenic bradycardia, or to minimize thecumulative effects on the heart's conduction system and myocardium ofepileptic seizures, especially in status epilepticus. Selective blockageof impulses traveling through a vagus nerve to the heart may beaccomplished with electrical stimulation to treat adverse cardiaceffects associated with disorders such as epilepsy, depression, diabetesor obesity. By blocking vagus nerve conduction to the heart, when thepatient's heart rate is incommensurate with the activity level orkinetic indices, a therapy may be provided to revert the change in heartrate (whether the change involves bradycardia or tachycardia). In oneembodiment, an electrical signal generator may be used to apply a firsttherapy signal to a vagus nerve of the patient, and an electrical signalgenerator (which may be the same or a different electrical signalgenerator) may apply a vagus nerve conduction blocking electrical signalto a vagus nerve (e.g., a cardiac branch of the vagus nerve) to blockcardiac effects that would result from the first electrical signal,absent the vagus nerve conduction blocking electrical signal.

Referring again to FIG. 9, the method may comprise determining thepatient's heart rate in response the therapy to determine whether theheart rate has been restored to a rate that is with commensurate withthe patient's activity level/kinetic index (940). If not, then thetherapy (e.g., VNS to reduce or increase heart rate to an appropriatevalue) may be continued, with or without parameter modification, orre-initiated after a delay period or confirmation period.

If the heart rate has returned to a range/value commensurate with theactivity level of the patient, the method may, in some embodiments,further involve determining whether or not an adverse event has occurred(950). Adverse events may include, without limitation, side effects suchas voice alteration, pain, difficulty breathing or other respiratoryeffects, adverse cardiac effects such as bradycardia (following adetermination of relative tachycardia in step 920), tachycardia(following a determination of bradycardia in step 920), and alterationin blood pressure or gastro-intestinal activity.

If an adverse event has occurred, the method may involve changing one ormore stimulation parameters to eliminate, reduce or ameliorate theadverse event (955). If no adverse event has occurred, the method maycomprise continuing to apply a signal the vagus nerve until apredetermined signal application duration has been reached (960), atwhich time the signal application may be stopped (970). The method mayfurther comprise determining, after the therapy has been stopped, if thepatient's heart rate remains incommensurate with the patient's activitylevel or type (980), in which case the signal application may be resumedor other appropriate action may be taken (e.g., local or remote alarmsor alerts, notification of caregivers/healthcare providers, etc.). Ifthe heart rate has returned to a value that is commensurate orappropriate for the patient's activity level, the signal application maybe discontinued (990).

FIG. 10 is a flow diagram of a method of treating a patient to withepilepsy by providing closed-loop vagus nerve stimulation to treatrelative tachycardia or relative bradycardia by restoring the patient'sheart rate to a rate that is commensurate with the activity type orlevel of the patient (e.g., as determined from a kinetic signal from asensing element such as a triaxial accelerometer or by measuring oxygenconsumption). In one embodiment, the method comprises identifyinginstances of relative tachycardia or relative bradycardia and respondingwith negative or positive chronotropic actions to restore the heart rateto a level commensurate with the patient's activity type or level.

In one embodiment, the method involves determining a heart rate and anactivity type or level for the patient (1010). The patient's heart ratemay be determined from an acquired cardiac signal or from stored data.The activity level or type of the patient may be determined from one ormore sensor or from stored data. Sensors may include, for example,accelerometers, positional sensors, GPS devices coupled to a clock,postural sensors, and metabolic sensors. Sensor data may be subject toconventional signal processing, and may in addition be adapted ormodified as a function of age, gender, body mass index, fitness level ortime of day or other indices of the patient's condition or environment.

The patient's activity type or level may then be used to determine oneor more heart rate ranges or values that are commensurate with theactivity type or level (1020). In some embodiments, heart rate rangesmay be established for particular levels or types of activity (e.g.,running, walking), that may be adaptively adjusted depending uponvarious factors such as the duration of the activity, the patient'sfitness level, the time of day, a level of fatigue, an environmentaltemperature, etc. A commensurate heart rate is one that is withinexpected ranges or values for the person's effort, and for factorsinherent to the patient and the environment.

If the heart rate is commensurate with the activity level, in oneembodiment no action may be taken, and the method may involve continuingto analyze the patient's cardiac and activity. On the other hand, if theheart rate is outside the identified value or range of valuesappropriate for the patient's activity type or level then the heart rateis not commensurate with the kinetic signal of the patient. Where thisis the case, the method may further comprise determining whether thepatient is experiencing relative tachycardia or is experiencing relativebradycardia (1030, 1040).

Where the heart rate of the patient is higher than a value commensuratewith the activity level or type, the patient is experiencing relativetachycardia (1030), and the method may comprise initiating a negativechronotropic action (1035) to slow the heart rate to a rate that iscommensurate with the activity level or type. In one embodiment, thismay involve applying stimulation to one or more of a left or right mainvagal trunk or cardiac branch of the patient. In other embodiments, themethod may comprise providing a drug to enhance the parasympathetic toneof the patient. In still other embodiments, the method may comprisereducing the patient's sympathetic tone, such as by applyinghigh-frequency stimulation to a sympathetic nerve trunk or ganglion oradministering an anti-cholinergic drug. Negative chronotropic actionsmay be used to treat epileptic seizures associated with tachycardia, andother medical conditions associated with relative tachycardia given thepatient's activity level.

Where the heart rate of the patient is lower than a value commensuratewith the activity level or type, the patient is experiencing relativebradycardia (1040), and the method may comprise initiating a positivechronotropic action (1045) to increase the heart rate to a rate that iscommensurate with the activity level or type. In one embodiment, thismay involve applying high-frequency (>>300 Hz) electrical stimulation toone or more of a left or right main vagal trunk or cardiac branch of thepatient to reduce the transmission of intrinsic vagus nerve actionpotentials in at least some vagal fibers. In other embodiments, themethod may comprise providing a drug to reduce the parasympathetic toneof the patient. In still other embodiments, the method may compriseincreasing the patient's sympathetic tone, such as by applyingelectrical signals to a sympathetic nerve trunk or ganglion or byadministering a sympatho-mimetic drug. Positive chronotropic actions maybe used to treat epileptic seizures associated with bradycardia, andother medical conditions associated with relative bradycardia given thepatient's activity level.

The method may further comprise, after initiating the negative orpositive chronotropic action, determining whether the patient's heartrate has been restored to a rate that is with commensurate with thepatient's activity level/kinetic index (1050). If not, then the therapy(e.g., VNS to reduce or increase heart rate to an appropriate value) maybe continued, with or without parameter modification, or re-initiatedafter a delay period or confirmation period.

If the heart rate has returned to a range/value commensurate with theactivity level of the patient, the method may, in some embodiments,further involve determining whether or not an adverse event has occurred(1060). Adverse events may include, without limitation, side effectssuch as voice alteration, pain, difficulty breathing or otherrespiratory effects, adverse cardiac effects such as bradycardia(following a determination of relative tachycardia in step 1030), ortachycardia (following a determination of bradycardia in step 1040), andalteration in blood pressure or gastric activity.

If an adverse event has occurred, the method may involve changing one ormore stimulation parameters to eliminate, reduce or ameliorate theadverse event (1070). If no adverse event has occurred, the method maycomprise continuing to stimulate the vagus nerve (or a chemical, thermalor mechanical therapy) until a predetermined stimulation duration hasbeen reached (1075), at which time the stimulation may be stopped(1080). The method may further comprise determining, after the therapyhas been stopped, if the patient's heart rate remains incommensuratewith the patient's activity level or type (1090), in which case thestimulation may be resumed or other appropriate action may be taken(e.g., local or remote alarms or alerts, notification ofcaregivers/healthcare providers, use of other forms of therapy, etc.).If the heart rate has returned to a value that is commensurate orappropriate for the patient's activity level, the stimulation may bediscontinued (1095).

Additional embodiments consistent with the foregoing description andfigures may be made. Non-limiting examples of some such embodiments areprovided in the numbered paragraphs below.

100. A method of controlling a heart rate of an epilepsy patientcomprising:

sensing at least one of a kinetic signal and a metabolic signal of thepatient;

analyzing the at least one of a kinetic and a metabolic signal todetermine at least one of a kinetic index and a metabolic index;

receiving a cardiac signal of the patient;

analyzing the cardiac signal to determine the patient's heart rate;

determining if the patient's heart rate is commensurate with the atleast one of a kinetic index and a metabolic index; and

applying an electrical signal to a vagus nerve of the patient based on adetermination that the patient's heart rate is not commensurate with theat least one of a kinetic signal and a metabolic signal of the patient.

101. The method of numbered paragraph 100, wherein determining at leastone of a kinetic index and a metabolic index comprises determining atleast one of an activity level or an activity type of the patient basedon the at least one of a kinetic index and a metabolic index, and

wherein determining if the patient's heart rate is commensurate with theat least one of a kinetic index and a metabolic index of the patientcomprises determining if the heart rate is commensurate with the atleast one of an activity level or an activity type.

102. The method of numbered paragraph 101,wherein determining if thepatient's heart rate is commensurate with the at least one of a kineticindex and a metabolic index comprises determining if the patient's heartrate is above or below a rate that is commensurate with the one or moreof a kinetic index and a metabolic index.

103. A method of treating a patient having epilepsy comprising

sensing at least one body signal of the patient;

determining whether or not the patient is having or has had an epilepticseizure based on the at least one body signal;

sensing a cardiac signal of the patient;

determining whether or not the seizure is associated with a change inthe patient's cardiac signal;

applying a first therapy to a vagus nerve of the patient based on adetermination that the patient is having or has had an epileptic seizurethat is not associated with a change in the patient's cardiac signal,wherein the first therapy is selected from an electrical, chemical,mechanical, or thermal signal; and

applying a second therapy to a vagus nerve of the patient based on adetermination that the patient is having or has had an epileptic seizureassociated with a change in the patient's cardiac signal, wherein thesecond therapy is selected from an electrical, chemical, mechanical(e.g., pressure) or thermal signal.

104. The method of numbered paragraph 103, further comprising applying athird therapy to a vagus nerve of the patient based a determination thatthe patient is not having or has not had an epileptic seizure, whereinthe third therapy is selected from an electrical, chemical, mechanicalor thermal signal.

105. A method of treating a patient having epilepsy comprising:

coupling a first set of electrodes to a main trunk of the left vagusnerve of the patient;

coupling a second set of electrodes to a main trunk of the right vagusnerve of the patient;

providing an electrical signal generator coupled to the first electrodeset and the second electrode set;

receiving at least one body data stream;

-   -   analyzing the at least one body data stream using a seizure        detection algorithm to determine whether or not the patient is        having and/or has had an epileptic seizure;    -   applying a first electrical signal from the electrical signal        generator to the main trunk of the left vagus nerve, based on a        determination that the patient is having and/or has had an        epileptic seizure without a heart rate change; and    -   applying a second electrical signal from the electrical signal        generator to the main trunk of the right vagus nerve, based on a        determination that the patient is having or has had an epileptic        seizure with a heart rate change.

106. A method of treating a patient having epilepsy comprising:

-   -   receiving at least one body data stream;    -   analyzing the at least one body data stream using a seizure        detection algorithm to detect whether or not the patient has had        an epileptic seizure;    -   receiving a cardiac signal of the patient;    -   analyzing the cardiac signal to determine a first cardiac        feature;    -   applying a first electrical signal to a vagus nerve of the        patient, based on a determination that the patient has not had        an epileptic seizure characterized by a change in the first        cardiac feature, wherein the first electrical signal is not a        vagus nerve conduction blocking electrical signal; and    -   applying a second electrical signal to a vagus nerve of the        patient, based on a determination that the patient has had an        epileptic seizure characterized by a change in the cardiac        feature, wherein the second electrical signal is a pulsed        electrical signal that blocks action potential conduction in the        vagus nerve.

107. A method of treating a patient having epilepsy comprising:

-   -   receiving at least one body data stream;    -   analyzing the at least one body data stream using a seizure        detection algorithm to detect whether or not the patient has had        an epileptic seizure;    -   receiving a cardiac signal of the patient;    -   analyzing the cardiac signal to determine a first cardiac        feature;    -   applying a first electrical signal to a vagus nerve of the        patient, based on a determination that the patient has not had        an epileptic seizure characterized by a change in the first        cardiac feature, wherein the first electrical signal is a pulsed        electrical signal that blocks action potential conduction in the        vagus nerve; and    -   applying a second electrical signal to a vagus nerve of the        patient, based on a determination that the patient has had an        epileptic seizure characterized by a change in the cardiac        feature, wherein the second electrical signal is not a vagus        nerve conduction blocking electrical signal.

In FIG. 11, a graph of heart rate versus time is shown, according to oneembodiment. A first graph 1100 includes a y-axis 1102 which representsheart rate where the heart rate goes from a zero value to an Nth value(e.g., 200 heart beats, etc.). Further, the first graph 1100 includes anx-axis 1104 which represents time from 1 minute to Nth minutes (and/or0.001 seconds to Nth seconds). In this example, a first heart rateversus time line 1106 for the patient is shown. In this example, thepatient's heart rate goes from 80 heart beats per minute to 118 heartbeats per minute with a first rise 1108A and a first run 1108B during afirst event 1108C. In addition, the patient's heart rate goes from 70heart beats per minute to 122 heart beats per minute during a secondevent 1108D which has a first percentage change 1110 associated with thesecond event 1108D. Further, the patient's heart rate goes from 70 beatsper minute to 113 beats per minute during an nth event 1108E whichsurpasses a first threshold amount 1112, and/or a second thresholdamount 1114, and/or an Nth threshold amount 1116. In one example, onlythe Nth threshold amount 1116 needs to be reached to trigger a therapyand/or an alert. In another example, only the second threshold amount1114 needs to be reached to trigger a therapy and/or an alert. Inanother example, only the first threshold 1112 needs to be reached totrigger a therapy and/or an alert. In another example, both the Nththreshold 1116 and the second threshold 1114 need to reached to triggera therapy and/or an alert. In another example, all of the Nth threshold1116, the second threshold 1114 and the first threshold 1112 need toreached to trigger a therapy and/or an alert. In one example, only theNth threshold amount 1116 needs to be reached during a specific timeperiod to trigger a therapy and/or an alert. In another example, onlythe second threshold amount 1114 needs to be reached during a specifictime period to trigger a therapy and/or an alert. In another example,only the first threshold 1112 needs to be reached during a specific timeperiod to trigger a therapy and/or an alert. In another example, boththe Nth threshold 1116 and the second threshold 1114 need to reachedduring a specific time period to trigger a therapy and/or an alert. Inanother example, all of the Nth threshold 1116, the second threshold1114 and the first threshold 1112 need to reached during a specific timeperiod to trigger a therapy and/or an alert. In these examples, one ormore triggering events may occur based on a determination of the riseand run of a change in heart rate, a percentage change in heart rate, athreshold amount being reached or exceeded (or within any percentage ofthe threshold), and/or any combination thereof. A triggering event mayinitiate one or more actions to increase and/or decrease the patient'sheart rate. For example, if the patient's heart rate is increasing whichdetermines the triggering event, then the system, device, and/or methodmay initiate one or more actions to decrease the heart rate of thepatient to help reduce, dampen, eliminate, and/or buffer the increase inthe patient's heart rate. Further, the system, device, and/or method mayoscillate between decreasing the patient's heart rate and increasing thepatient's heart rate depending on any changes to the patient's heartrate. For example, the system, device, and/or method may initiate one ormore actions to decrease a patient's heart rate based on the patient'sheart rate going from 80 heart beats per minute to 130 heart beats perminute which results in the patient's heart rate falling from 130 heartbeats per minute to 65 heart beats per minute in a first time period.Based on the change in the heart rate from 130 heart beats per minute to65 heart beats per minute in the first time period, the system, device,and/or method may initiate one or more actions to increase the patient'sheart rate and/or stabilize the patient's heart rate. In anotherexample, the system, method, and/or device may stop and/or modify anyinitiated action based on one or more feedback signals. In addition, oneor more warnings may be transmitted to the patient, a caregiver, adoctor, a medical professional, and/or logged.

In FIG. 12, another graph of heart rate versus time is shown, accordingto one embodiment. A second graph 1200 illustrating a second heart rateversus time line 1202 for the patient is shown. In this example, thepatient's heart rate goes from 80 heart beats per minute to 120 heartbeats per minute which creates a first system alert event 1204 (e.g.,A1). Further, the system, device, and/or method initiates a firsttherapy 1206 (e.g., X1) based on the first system alert event 1204. Inaddition, a second system alert event 1208 (e.g., A2) occurs and asecond therapy 1210 (e.g., X2) is initiated based on the second systemalert event 1208. In addition, a third system alert event 1212 (e.g.,A3) occurs and a third therapy (e.g., X3) 1214 is initiated based on thethird system alert event 1212 (e.g., A3). In addition, a fourth systemalert event 1216 (e.g., A4) occurs and a fourth therapy 1218 (e.g., X4)is initiated based on the fourth system alert event 1216 (e.g., A3).Further, a fifth therapy 1220 (e.g., X5) is initiated based on theeffects of the fourth therapy 1218 (e.g., X4). In addition, a fifthsystem alert event 1222 (e.g., A5) occurs and a sixth therapy (e.g., X6)1224 is initiated based on the fifth system alert event 1222 (e.g., A5).In addition, a sixth system alert event 1226 (e.g., A6) occurs and aseventh therapy (e.g., X7) 1228 is initiated based on the sixth systemalert event 1226 (e.g., A6). In addition, a seventh system alert event1230 (e.g., A7) occurs and an eighth therapy (e.g., X8) 1232 isinitiated based on the seventh system alert event 1230 (e.g., A7). Inaddition, a first stop stimulation event 1234 (e.g., B1) occurs whichturns off all therapies and/or system alerts may occur when the heartrate returns to the approximate starting heart rate and/or a targetvalue. In these examples shown with FIG. 12, a rise over run heart ratecalculation was completed to determine the one or more system alerts.However, it should be noted that any calculation (e.g., % increase, %decrease, etc. can be utilized). Further, all systems alerts and/ortherapies may occur as independent events and/or examples. For example,the seventh system alert may be the first system alert in a specificexample. In other words, no other events and/or therapies occurredbefore the seventh system alert. Therefore, the seventh system alertbecomes the first system alert. In addition, one or more warnings may betransmitted to the patient, a caregiver, a doctor, a medicalprofessional, and/or logged. In addition, there may be up to an Nthalerts, an Nth stop stimulation (and/or therapy) event, and an Nththerapy in any of the examples disclosed in this document.

In FIG. 13, another graph of heart rate versus time is shown, accordingto one embodiment. A third graph 1300 illustrating a third heart rateversus time line 1302 for the patient is shown. In this example, thepatient's heart rate goes from 80 heart beats per minute to 116 heartbeats per minute which creates a first system alert event 1304 (e.g.,A1). Further, the system, device, and/or method initiates a firsttherapy 1306 (e.g., X1) based on the first system alert event 1304. Inaddition, a first stop stimulation event 1308 (e.g., B1) occurs whichturns off all therapies and/or system alerts occurs when the heart ratereturns to the approximate starting heart rate and/or a target value.Further, the patient's heart rate goes from 80 heart beats per minute to123 heart beats per minute which creates a second system alert event1310 (e.g., A2). Further, the system, device, and/or method initiates asecond therapy 1312 (e.g., X2) based on the second system alert event1310. In addition, a second stop stimulation event 1314 (e.g., B2)occurs which turns off all therapies and/or system alerts occurs whenthe heart rate returns to the approximate starting heart rate and/or atarget value. In these examples shown with FIG. 13, a percentage changein heart rate calculation was completed to determine the one or moresystem alerts. However, it should be noted that any calculation (e.g.,rise over run, etc. can be utilized). Further, all systems alerts and/ortherapies may occur as independent events and/or examples. For example,the second system alert may be the first system alert in a specificexample. In other words, no other events and/or therapies occurredbefore the second system alert. Therefore, the second system alertbecomes the first system alert. In addition, one or more warnings may betransmitted to the patient, a caregiver, a doctor, a medicalprofessional, and/or logged.

In FIG. 14, another graph of heart rate versus time is shown, accordingto one embodiment. A fourth graph 1400 illustrating a fourth heart rateversus time line 1402 for the patient is shown. In this example, thepatient's heart rate goes from 80 heart beats per minute to 120 heartbeats per minute which creates a first system alert event 1404 (e.g.,A1) because the 120 heart beats per minutes meets or exceeds a firstthreshold value 1416 (e.g., 115 heart beats per minute). In thisexample, a second system alert event 1406 (e.g., A2) is created becausethe heart beats of the patient meets or exceeds the first thresholdvalue 1416 (e.g., 115 heart beats per minute). Further, the system,device, and/or method initiates a first therapy 1408 (e.g., X1) based onthe first system alert event 1404 and the second system alert event 1406occurring. The first system alert event 1404 and the second system alertevent 1406 may be time dependent. For example, the first system alertevent 1404 and the second system alert event 1406 may have to occurwithin a first time period for the initiation of the first therapy 1408.In another example, the first system alert event 1404 and the secondsystem alert event 1406 may not be time dependent. Further, a thirdsystem alert event 1410 (e.g., A3) is created because the heart beats ofthe patient meets or exceeds (and/or within a specific rate of thethreshold—in this example within 5 percent—heart rate is 110) the firstthreshold value 1416 (e.g., 115 heart beats per minute). Further, thesystem, device, and/or method initiates a second therapy 1412 (e.g., X2)based on the first system alert event 1404, the second system alertevent 1406, and/or the third system event occurring. It should be notedthat the second therapy 1412 has a time delay factor utilized with thesecond therapy 1412. In another example, no time delay is utilized. Inaddition, one or more time delays can be used with any therapy, anywarning, and/or any alert in this document. The first system alert event1404, the second system alert event 1406, and the third system alertevent 1410 may be time dependent. For example, the first system alertevent 1404, the second system alert event 1406, and the third systemalert event 1410 may have to occur within a first time period for theinitiation of the second therapy 1412. In another example, the firstsystem alert event 1404, the second system alert event 1406, and thethird system alert event 1410 may not be time dependent. Further, afirst stop stimulation event 1414 (e.g., B1) occurs which turns off alltherapies and/or system alerts occurs when the heart rate returns to theapproximate starting heart rate and/or a target value. Further, allsystems alerts and/or therapies may occur as independent events and/orexamples. For example, the third system alert may be the first systemalert in a specific example. In other words, no other events and/ortherapies occurred before the third system alert. Therefore, the thirdsystem alert becomes the first system alert. In addition, one or morewarnings may be transmitted to the patient, a caregiver, a doctor, amedical professional, and/or logged.

In FIG. 15, another graph of heart rate versus time is shown, accordingto one embodiment. A fifth graph 1500 illustrating a fifth heart rateversus time line 1502 for the patient is shown. In this example, thepatient's heart rate goes from 80 heart beats per minute to 40 heartbeats per minute which creates a first system alert event 1504 (e.g.,A1) because the 40 heart beats per minutes meets or exceeds a firstthreshold value 1520 (e.g., 50 heart beats per minute). It should benoted that no alert was generated when the heart rate fell to 52 heartbeats per minute because 52 heart beats per minute is above thethreshold value of 50 heart beats per minute. Further, the system,device, and/or method initiates a first therapy 1506 (e.g., X1) based onthe first system alert event 1504 occurring. Further, the patient'sheart rate goes from 80 heart beats per minute to 50 heart beats perminute which creates a second system alert event 1508 (e.g., A2) becausethe 50 heart beats per minutes meets or exceeds the first thresholdvalue 1520 (e.g., 50 heart beats per minute). Further, the system,device, and/or method initiates a second therapy 1510 (e.g., X2) basedon the second system alert event 1508 occurring. Further, a first stopstimulation event 1512 (e.g., B1) occurs which turns off all therapiesand/or system alerts occurs when the heart rate returns to theapproximate starting heart rate and/or a target value. In addition, thepatient's heart rate goes from 80 heart beats per minute to 45 heartbeats per minute which creates an nth system alert event 1514 (e.g., A3)because the 45 heart beats per minutes meets or exceeds the firstthreshold value 1520 (e.g., 50 heart beats per minute). Further, thesystem, device, and/or method initiates an Nth therapy 1516 (e.g., X3)based on the nth system alert event 1514 occurring. Further, an nth stopstimulation event 1518 (e.g., B2) occurs which turns off all therapiesand/or system alerts occurs when the heart rate returns to theapproximate starting heart rate and/or a target value. Further, allsystems alerts and/or therapies may occur as independent events and/orexamples. For example, nth system alert event 1514 alert may be thefirst system alert in a specific example. In other words, no otherevents and/or therapies occurred before nth system alert event 1514.Therefore, nth system alert event 1514 becomes the first system alert.In addition, one or more warnings may be transmitted to the patient, acaregiver, a doctor, a medical professional, and/or logged.

In regards to FIGS. 11-15 as related to this disclosure, the systems,devices, and/or methods may use a base line heart rate for the patient(e.g., a specific patient Bob, a general patient John Doe with a firsthealth condition, a first age, etc.) over a first time period (e.g. oneweek, one month, one year, etc.), 50 percentile of all measured heartrates, an average of all heart rates, and/or any other method ofdetermine a baseline heart rate. Further, the threshold level may bedetermined based on being the 40 percentile of the baseline, 39percentile of the baseline, 38 percentile of the baseline, . . . , 10percentile of the baseline, . . . , etc. In addition, the thresholdlevel may be determined based on being the 75 percentile of thebaseline, 76 percentile of the baseline, 77 percentile of the baseline,. . . , 90 percentile of the baseline, . . . , 99 percentile of thebaseline, . . . , etc. In one example, the threshold value may be the 75percentile of every recorded heart rate data. In another example, theoscillation does not matter whether the heart rate change is in anincreasing direction or a decreasing direction. In various examples, thesystems, devices, and/or method may reduce an amplitude of change (e.g.,damping the change in heart rate) to enhance system performance and/orto reduce side effects. In addition, the determination of one or moreside effects may initiate a reduction in therapy, a stoppage of therapy,a modification of therapy (e.g., changing a therapy that reduces heartrate to another therapy that increases heart rate), one or morewarnings, and/or one or more logging of data.

In FIG. 16, a flowchart of a therapy procedure is shown, according toone embodiment. A method 1600 includes obtaining one or more data pointsand/or characteristics relating to heart rate of a patient (step 1602).The method 1600 may also include determining a monitored value based onethe obtained one or more data points and/or characteristics relating tothe heart rate (step 1604). The method 1600 may further compare themonitored value to one or more threshold values (step 1606). The method1600 may via one or more processors (of a medical device(s) and/ormedical device system) determine whether a triggering event has occurred(step 1608). If no triggering event has occurred, then the method 1600moves back to step 1602. If a triggering event has occurred, then themethod 1600 may determine via one or more processors (of a medicaldevice(s) and/or medical device system) whether an action whichincreases heart rate should be implemented (step 1610). If an actionwhich increases heart rate should be implemented, then the method 1600may increase a sympathetic tone via one or more actions and/or decreasea parasympathetic tone via one or more actions and/or implement anotheraction which increases heart rate (step 1612). After the implements ofone or more actions, the method 1600 returns to step 1602. If an actionwhich increases heart rate should not be implemented, then the method1600 may determine via one or more processors (of a medical device(s)and/or medical device system) whether an action which decreases heartrate should be implemented (step 1614). If an action which decreasesheart rate should be implemented, then the method 1600 may decrease asympathetic tone via one or more actions and/or increase aparasympathetic tone via one or more actions and/or implement anotheraction which decreases heart rate (step 1616). After the implements ofone or more actions, the method 1600 returns to step 1602.

In one embodiment, a system for treating a medical condition in apatient includes: a sensor for sensing at least one body data stream; aheart rate unit capable of determining a heart rate of the patient basedon the at least one body data stream; and a logic unit configured viaone or more processors to compare a monitored value which is determinedbased on one or more data points relating to the heart rate to one ormore threshold values, the logic unit further configured to determine atriggering event based on the comparison. Further, the one or moreprocessors may initiate one or more actions to change the heart rate ofthe patient based on the determination of the triggering event.

In another example, the system includes at least one electrode coupledto a vagus nerve of the patient and a programmable electrical signalgenerator. In another example, the one or more processors may increase asympathetic tone to increase the heart rate of the patient. In anotherexample, the one or more processors may decrease a parasympathetic toneto increase the heart rate of the patient. In another example, the oneor more processors may decrease a sympathetic tone to decrease the heartrate of the patient. In another example, the one or more processors mayincrease a parasympathetic tone to decrease the heart rate of thepatient. In another example, the system includes a seizure detectionunit which analyzes the at least one body data stream to determine anepileptic seizure status. In another example, the system includes atleast one electrode coupled to a vagus nerve of the patient and aprogrammable electrical signal generator. Further, the one or moreprocessors may apply an electrical signal to the vagus nerve of thepatient based on a determination that a seizure is characterized by adecrease in the heart rate of the patient where the electrical signal isapplied to block action potential conduction on the vagus nerve.

In another embodiment, a system for treating a medical condition in apatient, includes: a sensor for sensing at least one body data stream;at least one electrode coupled to a vagus nerve of the patient; aprogrammable electrical signal generator; a heart rate unit capable ofdetermining a heart rate of the patient based on the at least one bodydata stream; and a logic unit configured via one or more processors tocompare a monitored value which is determined based on one or more datapoints relating to the heart rate to one or more threshold values, thelogic unit further configured to determine a triggering event based onthe comparison. Further, the one or more processors may initiate one ormore actions to change the heart rate of the patient based on thedetermination of the triggering event.

In another example, the one or more processors may increase asympathetic tone to increase the heart rate of the patient based on afirst triggering event. Further, the one or more processors may decreasea sympathetic tone to decrease the heart rate of the patient based on asecond triggering event. Further, the one or more processors maydecrease a parasympathetic tone to increase the heart rate of thepatient based on a third triggering event. Further, the one or moreprocessors may increase a parasympathetic tone to decrease the heartrate of the patient based on a fourth triggering event.

In another example, the one or more processors may increase thesympathetic tone to increase the heart rate of the patient based on asecond triggering event. Further, the one or more processors mayincrease the sympathetic tone to increase the heart rate of the patientbased on a third triggering event. Further, the one or more processorsincrease the sympathetic tone to increase the heart rate of the patientbased on an nth triggering event.

In another example, the one or more processors decrease a sympathetictone to decrease the heart rate of the patient based on a firsttriggering event. Further, the one or more processors decrease thesympathetic tone to decrease the heart rate of the patient based on asecond triggering event. Further, the one or more processors maydecrease the sympathetic tone to decrease the heart rate of the patientbased on a third triggering event. In addition, the one or moreprocessors decrease the sympathetic tone to decrease the heart rate ofthe patient based on an nth triggering event.

Cardio-protection in epilepsy is a rapidly growing field of vitalimportance. In this disclosure, systems, devices, and/or method ofprotecting the heart from standstill or fatal arhythmias are disclosed.Further in this disclosure, systems, devices, and/or methods ofautomated detections, warnings, reportings, treatments, controls and/orany combination thereof of ictal and peri-ictal chronotropic instabilityare shown.

In FIG. 17, a graph shows monotonic increase and decrease in heart rate.In FIG. 17, a first triggering event, a first warning event, and/or afirst therapy event 1702 are shown. Further, a second triggering event1704, a second warning event, and/or a second therapy event 1704 areshown. In addition, an Nth triggering event, an Nth warning event,and/or an Nth therapy event 1706 are shown. In FIG. 18, the heart rateof the patient increases which is followed by a decrease in heart rate,then an increase heart rate and a final decrease in heart rate. In thisexample, the first drop in heart rate crossed downwardly the detectionthreshold which would have temporarily disabled the warning system andthe delivery of the therapy. While the first peak was not temporallycorrelated with paroxysmal activity on any of the intra-cranialelectrodes used in this patient, it is likely that the first increase inheart rate was caused by epileptic discharges from a brain site that wasnot being investigated. In this example, the x-axis is time in hours andthe y-axis is heart beats per minute. In this example, an electrographiconset in the brain 1810 is shown and an electrographic termination inthe brain 1812 is shown.

In FIG. 19, a change in ictal heart rate is shown. In this example, thedrop in heart rate during the seizure, is even more prominent that theone depicted in FIGS. 17-18, as it is below the inter-ictal baseline. Itshould be noted that the oscillations in heart rate during thepost-ictal period are indicative of cardiac instability. In thisexample, a seizure onset point 1910 and a seizure termination point 1912are shown.

In FIG. 20, large amplitude tachycardia cycles occurringquasi-periodically after termination of paroxysmal activity recordedwith intra-cranial electrodes. While the mechanisms responsible forthese oscillations are unknown, the probability that they are epilepticin nature cannot be excluded, since electrographic and imaging data usedto guide intra-cranial electrode placement pointed to the existence ofonly one epileptogenic site.

In FIG. 21, small amplitude continuous quasi-periodic oscillationspreceding and following a seizure recorded with intra-cranial electrodes(same patient as FIG. 20). In various embodiments, ictal and peri-ictalcardiac instability are shown. The mechanisms leading to SUDEP have notbeen elucidated, in part due to the inability to record data during thecritical events that culminate in cardiac fibrillation or in standstill(or in respiratory arrest). In this example, a first triggering event, afirst warning event, and/or a first therapy event 2102 are shown.Further, an Nth triggering event, an Nth warning event, and/or an Nththerapy event 2104 are shown.

The data obtained in intractable epileptics undergoing epilepsy surgeryevaluation not only supports a cardiac mechanism (of course, not at theexclusion of catastrophic respiratory failure) but more specificallypoints to chronotropic instability as backdrop against which, lethalarrhythmias or cardiac standstill may ensue. Moreover, the instabilityis not restricted to the ictal period but, in certain cases, precedesand/or follows it for several minutes. FIGS. 17-21 illustrate thespectrum of instability in intractable epileptics. This phenomenon isreferred herein to as Ictal and Pre-Ictal Chronotropic Instability.

The challenges that for accurate quantification and delivery ofefficacious therapies, ictal chronotropic instability poses, wereaddressed and strategies to manage them are outlined. Here, theattention is focused on Ictal and Pre-Ictal Chronotropic Instability, amore prolonged and serious pathological phenomenon in intractableepileptics and on the vital issues of cardio-protection.

The aim of this disclosure is to contingently and adaptively dampenbased on the slope, amplitude, duration and “direction” (positive ornegative chronotropic and its magnitude relative to an adaptivebaseline/reference heart rate) the heart oscillations present before,during or after epileptic seizures.

While several embodiments may be envisioned, on embodiment (forefficacy, practicality and cost-effectiveness) is to electricallystimulate/activate the trunk or a branch of the right vagus nerve in thecase of elevations in heart (to reduce the heart rate, when there aremore than 2 consecutive oscillations/cycles or 1 that is large andprolonged. The intensity and duration of stimulation as well as otherparameters are determined by the slope, amplitude and duration of theoscillations, while ensuring adequate blood perfusion to all organs. Inthe case of negative chronotropic effects (decreases in heart rate) thetrunk or a branch of the right vagus nerve may be “blocked” usingcertain electrical stimulation techniques or through cooling; the effectof this intervention is to increase heart rate.

In one embodiment, the “height” of the oscillation is the only featureconsidered. While obviously important, this embodiment does not takeinto consideration a possibly more important feature: the rate at whichthe oscillation occurs: the consequences of waiting to intervene untilan oscillation reaches a certain height (e.g., 120 bpm) are different ifit takes, 30 seconds for the heart rate to reach the value than if ittakes 2 seconds to reach the value. Estimating the rate of change of theheart rate, provides life-saving information. Another aspect is theinter-maxima or inter-minima interval between oscillations. Having heartrate oscillation occur every 2-3 seconds is much more serious than every1-2 hours. In one example, one benefit may be that the window to act islengthen which can save lives. In one embodiment, a system for treatinga medical condition in a patient includes: a sensor for sensing at leastone body data stream; a heart rate unit which determines a heart rateand a heart rate oscillation of the patient based on the at least onebody data stream; and a logic unit which compares via one or moreprocessors a monitored value which is determined based on one or moredata points relating to the heart rate and to the heart rate oscillationto a threshold value, the logic unit determines a triggering event basedon the comparison where the one or more processors initiate one or moreactions to change the heart rate of the patient based on thedetermination of the triggering event.

In another example, the system includes at least one electrode coupledto a vagus nerve of the patient and a programmable electrical signalgenerator. Further, the one or more processors may increase asympathetic tone to increase the heart rate of the patient. In anotherexample, the one or more processors may decrease a parasympathetic toneto increase the heart rate of the patient. In another example, the oneor more processors may decrease a sympathetic tone to decrease the heartrate of the patient. Further, the one or more processors may increase aparasympathetic tone to decrease the heart rate of the patient. Inaddition, the system may include a seizure detection unit which analyzesthe at least one body data stream to determine an epileptic seizurestatus. The system may include at least one electrode coupled to a vagusnerve of the patient and a programmable electrical signal generatorwhere the one or more processors apply an electrical signal to the vagusnerve of the patient based on a determination that a seizure ischaracterized by a decrease in the heart rate of the patient and wherethe electrical signal is applied to block action potential conduction onthe vagus nerve. In addition, the heart unit may determine aninter-maxima interval and an inter-minima interval between a firstoscillation and a second oscillation. Further, the logic unit maycompare the inter-maxima interval and the inter-minima interval to aninterval threshold. In addition, the one or more processors may initiateone or more actions based on the interval threshold being reached.

The particular embodiments disclosed above are illustrative only as thedisclosure may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Furthermore, no limitations are intended to thedetails of construction or design herein shown other than as describedin the claims below. It is, therefore, evident that the particularembodiments disclosed above may be altered or modified and all suchvariations are considered within the scope and spirit of the disclosure.Accordingly, the protection sought herein is as set forth in the claimsbelow. In addition, all examples, embodiments, and/or elements may becombined in any manner that are disclosed in this document. In otherwords, an element from a first example (paragraph [0088]) can becombined with any other element, such as, a second element from an Nthexample (paragraph [0163]). For brevity, all these examples are notwritten out but are part of this document.

Illustrative embodiments of the disclosure are described herein. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. In the development of any such actualembodiment, numerous implementation-specific decisions must be made toachieve the design-specific goals, which will vary from oneimplementation to another. It will be appreciated that such adevelopment effort, while possibly complex and time-consuming, wouldnevertheless be a routine undertaking for persons of ordinary skill inthe art having the benefit of this disclosure.

This document does not intend to distinguish between components thatdiffer in name but not function. In the following discussion and in theclaims, the terms “including” and “includes” are used in an open-endedfashion, and thus should be interpreted to mean “including, but notlimited to.” Also, the term “couple” or “couples” is intended to meaneither a direct or an indirect electrical connection. “Direct contact,”“direct attachment,” or providing a “direct coupling” indicates that asurface of a first element contacts the surface of a second element withno substantial attenuating medium there between. The presence of smallquantities of substances, such as bodily fluids, that do notsubstantially attenuate electrical connections does not vitiate directcontact. The word “or” is used in the inclusive sense (i.e., “and/or”)unless a specific use to the contrary is explicitly stated.

The term “electrode” or “electrodes” described herein may refer to oneor more stimulation electrodes (i.e., electrodes for delivering atherapeutic signal generated by an IMD to a tissue), sensing electrodes(i.e., electrodes for sensing a physiological indication of a state of apatient's body), and/or electrodes that are capable of delivering atherapeutic signal, as well as performing a sensing function.

In one embodiment, the present disclosure provides a method of detectinga state change based upon data derivable from cardiac signals. The statechange can be, for example, at least one of an unstable brain state, abrain state indicative of an elevated probability of a state change, abrain state indicative of an impending state change, or a state change,among others.

In one embodiment, the present disclosure provides a method forindicating an occurrence of a state change. In one embodiment, themethod comprises obtaining a time series of cardiac data from a patient;determining a reference heart rate parameter from said cardiac data;determining a heart rate derivative shape from said time series ofcardiac data, wherein said heart rate derivative shape comprises atleast one characteristic selected from a number of phases relative tosaid reference heart rate parameter, a number of extrema of said heartrate derivative, a number of directions of change of said heart ratederivative, a number of positive phases, or a number of negative phases;and indicating an occurrence of a state change based upon adetermination that said heart rate derivative shape matches a statechange template in said at least one characteristic.

The cardiac data can be gathered by any of a number of techniques. Forexample, the cardiac data may be gathered by an electrocardiogram (EKG)device. For another example, the cardiac data may be gathered by acranial nerve stimulator device. In one embodiment, the cardiac data maybe related to the R-waves of the beat sequence, such as a time series ofR-waves or a series of R-R intervals. Those skilled in the art havingbenefit of the present disclosure would appreciate that other timeseries of cardiac waves and/or their fiducial points (e.g., P waves, Twaves, etc.) may be used and still remain within the spirit and scope ofthe present disclosure.

Data relating to R-waves may be gathered by an EKG device or, in oneembodiment, by a vagus nerve stimulator, such as described in U.S. Pat.No. 5,928,272, which is hereby incorporated by reference herein.

Obtaining the cardiac data may comprise sensing a time of beat sequenceof a patient's heart and generating a time series data stream from thetime of the beat sequence. In a further embodiment, receiving thecardiac data of the patient's heart may comprise sensing andtime-stamping a plurality of R waves, and generating the time seriesdata stream may comprise determining a series of R-R intervals from thetime stamps of the sensed R waves.

In one embodiment, the fiducial time marker is an R wave peak orthreshold crossing. The amplitude or height of one or morerepresentative R waves may be used to set a threshold that, when reachedor crossed, is registered as a fiducial time marker of a heart beat.

In one embodiment, a heart rate derivative is determined from the timeseries of cardiac data. As defined herein, a “heart rate derivative” isa value derivable, directly or indirectly, from the time series ofcardiac data, wherein the value relates to a feature, property orrelationship between two or more heart beats. Although a first orhigher-order derivative, as understood from calculus, is a “heart ratederivative” under the above definition, a heart rate derivative is notnecessarily a first or higher-order calculus derivative. Exemplary heartrate derivatives include, but are not limited to, heart rate and heartrate variability (HRV). A “shape” is used herein to refer to a featureapparent to the person of ordinary skill in the art upon viewing a graphof the heart rate or of one of its derivative over a period of time. Inone embodiment, a heart rate derivative shape comprises at least onecharacteristic selected from a number of phases relative to a referenceheart rate parameter, a number of extrema of the heart rate derivative,a number of directions of change of the heart rate derivative, a numberof positive phases, or a number of negative phases.

By “heart rate shape” is meant one or more characteristics or featuresof a time series of cardiac data that are reflective of the appearanceof that time series if plotted on a graph (on the y-axis and time on thex-axis). For example, one characteristic of heart rate shape is a numberof phases relative to the reference heart rate parameter. A “phase” is aperiod between two consecutive deviations from, crossings of, or returnsto the reference heart rate parameter. A phase may be positive (having avalue greater than the reference heart rate parameter) or negative(having a value less than the reference heart rate parameter). Yetanother exemplary characteristic of heart rate shape is a number ofextrema of heart rate. An “extremum” (plural, “extrema”) is a pointwhere the slope of heart rate changes sign, or phrased alternatively, apoint that is a highest high or lowest low of heart rate for some lengthof time or number of beats before and after. Still another exemplarycharacteristic of heart rate shape is a number of directions of heartrate change, which can be defined as the number of changes of the signof the slope of heart rate, plus one. Yet another exemplarycharacteristic of heart rate shape is the steepness of one or moreascending or descending slopes.

Though not to be bound by theory, we have found that heart activityduring normal states (exercise, anger, etc.) and abnormal states (e.g.,epileptic seizures) as displayed or graphed over various time scalestake on distinctive shapes which may be used to identify the variousstates as well as changes from one state to another, such as fromnon-seizure to seizure. Said shapes are considered and treated herein astemplates, given their stereotypical nature, and are used in severalways (to be described below) to detect states, state changes, stateand/or state change onsets, and/or other features, such as duration,intensity or magnitude, and/or other relevant characteristics, such astype of state or state change.

Another heart rate derivative that may be considered is a heart ratevolatility (non-stationarity) parameter, a measure of dispersion whichmay be defined as a change in the standard deviation or variance ofheart rate over a moving window. Commonly, the higher the volatility,the higher appears to be the probability of state changes. Volatility, ametric often found in financial contexts, is used here to obtain certaininformation about the state of a system regardless of the similaritiesor dissimilarities between financial and biological time series andconsideration for the underlying systems' dynamics.

For example, let . . . ^(t−2)Q, ^(t−1)Q, ^(t)Q, ^(t+1)Q, . . . be astochastic process. Its terms ^(t)Q represent heart rates as componentsof a vector or a matrix. The volatility of the process at time t¹ isdefined as the standard deviation of the time t return. Typically, logreturns are used, so the definition becomes

$\begin{matrix}{{volatility} = {{std}\left( {\log \left( \frac{\,^{t}Q}{\,^{t - 1}Q} \right)} \right)}} & \lbrack 1\rbrack\end{matrix}$

wherein log denotes a natural logarithm.

If heart rate time series are conditionally homoskedastic, definition[1] is precise. However, if they are conditionally heteroskedastic,measure [1] requires modification. Volatility at time f¹ represents inthis case, the standard deviation of the time t log return conditionalon information available at time f¹ as defined below

${volatility} = {{\,^{t - 1}{std}}\left( {\log \left( \frac{\,^{t}Q}{\,^{t - 1}Q} \right)} \right)}$

wherein the preceding superscript f¹ indicates that the standarddeviation is conditional on information available at time f¹.

Transitions from homoskedasticity (defined herein as approximatelyconstant standard deviations over a certain time window) toheteroskedasticity (inconstant standard deviation) also provideinformation about the probability of being in or near a state change ofinterest and may be used for automated detection, warning, delivery oftherapy and logging (of events, warnings and therapy) purposes.

Volatility will be measured using time scales (seconds to days) based ontemporal (e.g., duration) and other properties of the state change oninterest and of the reference state.

The method also comprises indicating an occurrence of a state changebased upon a determination that said heart rate derivative shape matchesa state change template in said at least one characteristic.

A “state change template” is a template known or discovered by thepractitioner to be associated with the state change, wherein thetemplate can be used in the analysis of the heart rate derivative shape.

Plots of instantaneous heart rate (y-axis) as a function of time(x-axis) in subjects with epilepsy reveal consistent changes before,during and after seizures, referred herein to as circum-ictal changes.(“Circum-ictal” or “circumictal,” as used herein, encompasses pre-ictal,ictal, and post-ictal subperiods. The circumictal period can beconsidered the time window (e.g., in min) preceding and following aseizure during which cardiac activity differs from that observed duringinterictal conditions, normal physical activity (including exercise),intense emotions (fear, anger, etc.), and physiological functions suchas defecation, urination or coitus). The curves described by thesecircum-ictal changes in heart rate, approximate triangles or parabolae,and may have indentations of varying sizes. See the discussion of FIGS.26-38B below for more information. Visual review of a large humandatabase of instantaneous heart rate plots reveal that over a certainwindow length (referred herein as the mesoscopic scale) theircircum-ictal shapes are limited to the triangles and parabolae and to“deformations” of these two shapes (see FIG. 26). These “deformations”appear to have temporal and magnitude dependencies, in that the longerthe duration of the change in heart rate and the larger its magnitude,the more likely they are to occur. The behavior of these shapes likelyreflect fluctuations in the strength of sympathetic and parasympatheticinputs to the heart. For example, transient, rapid drops in heart ratemay be caused by either a withdrawal in sympathetic tone or by anincrease in parasympathetic tone resulting from differential activationor inhibition by epileptiform activity of brain regions involved inautonomic control.

The shape (i.e., all the geometrical information that is invariant toposition (including rotation) and scale) of these curves may be used fordetection of changes in brain state such as epileptic seizures and theirproperties may be characterized through use of statistical shapeanalysis (e.g., Procrustes analysis), of the different embodiments of“matched filtering” or of other geometrical (Euclidian andnon-Euclidian) methods. Other approaches such as computing the area ofthe triangles and parabolae and comparing the results to a referencevalue outside the circum-ictal state[]may be used. In the case oftriangles, there area may be calculated using for example Heron'sformula:

Area=√{square root over (S(S−a)(S−b)(S−c))}, where

S=½(a+b+c) and a, b, and c are the sides of the triangle.

Similarly the area of parabolae (Area=⅔ b×h, where b is the base and theheight, may be computed and used to detect seizures.

Other attributes not captured by the concept of shape may be applied asneed to the sign al for detecting state changes such as epilepticseizures.

In one embodiment, the at least one characteristic of the state changetemplate comprises two or more phases relative to the reference heartrate parameter, two or more extrema of the heart rate derivative, threeor more directions of change of the heart rate derivative or its slope,a number of positive phases, or a number of negative phases, providedthe total number of positive phases and negative phases is two or more.

In another embodiment, the at least one characteristic of the statechange template comprises at least one phase relative to the referenceheart rate parameter, at least one extremum of the heart rate derivativeor its slope, two or more directions of change of the heart ratederivative, a number of positive phases, or a number of negative phases,provided the total number of positive phases and negative phases is atleast one.

In another embodiment, the at least one characteristic of the statechange template comprises at least one of the amplitude of at least onephase, the duration of at least one phase, the valence (positive ornegative) of at least one phase, at least one slope of at least onephase, the arc length (which is used interchangeably with line length)of at least one phase, the number of extrema in at least one phase, andthe sharpness of the extrema of at least one phase.

A reference heart rate parameter, as used herein, is a reference valueobtained during a state that is deemed of no or little interest forautomated detection, warning, treatment or logging purposes. Thereference heart rate parameter may be a single value, a series ofvalues, a statistical is selected from the group consisting of a shape,a vector, a vector space, a matrix and two or more thereof.

For example, heart activity during a non-seizure state is considered asa reference state. The reference heart rate parameter may be calculatedfrom a time series of value over any particular window, such as a windowhaving a length from 30 seconds to 24 hours, although longer or shorterwindows may be used. The window may be a simple window or anexponentially-forgetting window, as discussed in U.S. patentapplications Ser. No. 12/770,562, filed Apr. 29, 2010; Ser. No.12/771,727, filed Apr. 30, 2010; and Ser. No. 12/771,783, filed Apr. 30,2010; the disclosures of each hereby incorporated herein by reference.The reference heart rate parameter may be calculated as any measure ofany tendency of the time series, such as the central tendency of thetime series. For example, the reference heart rate parameter may becalculated as a mean, median, nth percentile (where n can be from 30 to70), or exponential moving average of the time series, among othermeasures of central tendency. Other mathematical or statisticalmeasures, including, but not limited to, correlation dimension, entropy,Lyapunov exponents, and fractal or multifractal dimensions, may be alsoapplied to any of the parameters or their templates.

The reference heart rate parameter may be determined from previouslyrecorded data, or from “normative” values obtained from normal orabnormal cohorts of subjects or populations or it may be determined fromthe time series of cardiac data referred to above.

An exemplary state change template can be derived from the pattern shownin FIGS. 29A-29B, wherein the changes in heart rate during a seizureform a readily discernible “A1” between 0.88 hours and 0.92 hours,having one positive phase relative to a reference heart rate parameter(calculated as the median value from about 0.85 hours to 0.89 hours andfrom about 0.93 hours to about 1.00 hour), three extrema (two maxima andone minimum, each being an extremum relative to about 20 seconds beforeand 20 seconds after), and four directions of heart rate change.

The state change template may be the “raw” pattern (analog or digitized)or it can be derived by smoothing, averaging, or otherwisemathematically processing subseries of cardiac data obtained duringstate changes. A “matched filter” is a type of filter matched to theknown or assumed characteristics of a target signal, to optimize thedetection of that signal in the presence of noise. A matched filter isthe filter with impulse response equal to the time reversed, complexconjugate impulse response of the input.

One skilled in the art will appreciate that when applying matched filtertechniques to attempt to detect a pattern in a signal, the raw signalmay first be transformed so that it has zero mean on a timescale ofinterest when the pattern is absent. Such transformation may include,but not be limited to, detrending or subtracting a background referencevalue (or time-varying reference signal) from the raw signal and is usedto remove bias in the matched filter output and improve itssignal-to-noise ratio.

Seizure detection may be performed over multiple time scales or windowlengths listed in no particular order:

a) “Mesoscopic” corresponding to a scale of observation of severalseconds to tens of seconds (e.g., 10-300 s) to capture at least in part,a change in the shape of heart rate plot representative of a statechange.

b) “Microscopic” corresponding to the scale of observation of at leastpart of a heart beat such as that represented by an EKG's P-QRS-Tcomplex.

c) “Macroscopic” corresponding to a scale of observation longer than 300s to encompass more than the information contained in the mesoscopicscale or window as defined in a).

Seizure detection at a macroscopic scale provides information notobtainable with the two other scales (micro- and mesoscopic) allowingfor the identification of certain patterns (defined herein as theoccurrence of more than one triangle or parabola or combinations thereofwithin a macroscopic window).

A shape deformation (e.g., a deformed “A1”) may show local and globalextrema that may be used for detection and validation purposes.

In one embodiment, the method comprises matched filtering. Matchedfiltering is a theoretical framework and not the name of a specificfilter. A matched filter is a type of filter matched to the known orassumed characteristics of a target signal and is designed to optimizethe detection of that signal in the presence of noise as it maximizesSN. A matched filter's impulse response is equal to the time reversed,complex conjugate impulse response of the input.

The output response of a “matched” filter derived from meso-, micro- ormacroscopic patterns, as it is passed through any of these patterns ischaracteristic (it forms a spatio-temporal pattern) and in turn may beused not only to validate detections but to allow detections before theconvolution is completed (‘early” detection).

A second filter matched to the first matched filter's output responsemay be run simultaneously with the first matched filter and its outputresponse may be used for early detection and second level validation ofthe detection.

The pattern formed by any of the cardiac activity parameters may be usedas a matched filter. Other realizations such as the orthogonal andprojected orthogonal matched filter detection (Eldar Y C. Oppenheim A,Egnor D. Signal Processing 2004; 84: 677-693), adaptive matched filterand parametric adaptive matched filter (Dong Y. Parametric adaptivefilter and its modified version DSTO-RR-0313 My 2006 AustralianGovernment, Dept. of Defence); the nearest matched filter forclassification of spatio-temporal patterns (Hecht- Nielsen R. AppliedOptics 1987; 26:1892-98), an outlier resistant matched filter (GerlachK. IEEE Trans Aerospace Electronic Syst 2002; 38:885-901), a phase-onlymatched filter (Homer J L, Gianino P D. Applied Optics 1984; 23:812-16)may be also used for detection and validation of state changes suchepileptic seizure.

The detection and validation of states based on the morphology or shapeof signals may be performed at various time scales (micro-, meso-, ormacroscopic) through estimation of the autocorrelation function of saidshapes or patterns. Furthermore, estimation of the autocorrelationfunction of a reference state may also be used for detection andvalidation of state changes alone or in combination with theautocorrelation estimates of the state change shapes or patterns.Autocorrelation may be considered as an equivalent method to matchedfiltering.

Other methods, such as non-linear detectors (Theiler J, Foy B R, FraserA M. Beyond the adaptive matched filter: Non-linear detectors for weaksignals in high dimensional clutter. Proc SPIE 6565 (2007) 6565-02:1-12) and maximum likelihood estimation (Forney G D, Maximum-likelihoodestimation of digital sequences in the presence of intersymbolinterference. IEEE Trans Information Theory 1972; 18:363-76), may bealso applied in this disclosure.

Matching a heart rate shape to a state change template can be performedby any appropriate mathematical technique. For example, pattern matchingby use of a matched filter is generally known to one skilled in the art.In one embodiment, the state change template comprises at least onematched filter. In one embodiment, a “match” refers to a match scorefound by a matched filter analysis of greater than about 0.75, such asgreater than about 0.80, greater than about 0.85, greater than about0.90, greater than about 0.95, greater than about 0.98, or greater thanabout 0.99. A “failure to match” refers to a match score found by amatched filter analysis of less than about 0.75, such as less than about0.80, less than about 0.85, less than about 0.90, less than about 0.95,less than about 0.98, or less than about 0.99. However, these values maybe changed as needed.

In one embodiment, the state change template comprises at least a statechange matched filter and a reference parameter matched filter. A“match” can be defined as a match to the state change matched filter notaccompanied by a match to the reference parameter filter.

Regardless of the type of filter, in one embodiment, the heart ratederivative shape has a matched filter score to said state changetemplate greater than a value threshold for at least a durationthreshold. For example, any of the values set forth above may be used asthe value threshold and the duration threshold may be selected as anyappropriate number of seconds or heart beats, such as 1 to 10 seconds,or 1 to 10 beats, such as 3 beats. 102891 In one embodiment, the statechange template exists in a first timescale and said heart ratederivative shape is present in said first timescale. For example, theheart rate derivative shape is present over a first timescale nottypically found in a reference heart rate derivative shape observedduring rising from lying to sitting, rising from sitting to standing,minor physical exertion, exercise, or emotionally-intense experiences.This allows distinction between heart rate derivative shapes associatedwith a state change of interest, e.g., an epileptic seizure, and heartrate derivative shapes associated with normal daily activities.

In one embodiment, the state change template comprises at least onepositive phase and at least one negative phase. In a further embodiment,the at least one positive phase is a period of elevated heart rate. Inan even further embodiment, the period of elevated heart rate is aperiod of tachycardia. In people fifteen years of age and older,tachycardia is defined as a heart rate greater than 100 bpm. In anotherfurther embodiment, the at least one negative phase is a period ofdecreased heart rate. In an even further embodiment, the period ofdecreased heart rate is a period of bradycardia. Bradycardia is definedin adults as a heart rate less than 60 bpm.

In one embodiment, the state change template comprises at least twoextrema of heart rate. In a further embodiment, the state changetemplate can also comprise at least two phases.

The state change template may comprise one or more shapes readilydiscernible to the human eye. For example, the state change template maycomprise a triangle, such as that shown in FIG. 27. Although in manycases, state change templates that appear more complex than a trianglemay be useful, they can generally be understood as involving one or moretriangles or parabolas and/or deformations thereof.

FIG. 26 illustrates the metamorphosis or transformation of circumictalheart rate shapes or patterns at a mesoscopic scale. The simplest shapeis that of a parabola (left upper panel). In certain seizures ashort-lived withdrawal or reduction of sympathetic influences or anincrease in parasympathetic ones early in the course of a seizure causesa notch or indentation in the parabola (right upper panel). In otherseizures (in the same subject or in a different subject), a later, morepronounced and prolonged withdrawal or reduction of sympatheticinfluences or an increase in parasympathetic ones (compared to that seenin the right upper panel) leads to a prominent indentation or notch(right lower panel), resembling the letter “M”. A later, briefer, andless pronounced withdrawal or reduction of sympathetic influences or anincrease in parasympathetic ones (compared to that seen in the rightlower panel) causes an indentation in the parabola.

The relative balance of sympathetic and parasympathetic influences canbe assayed at multiple timescales. As can be seen with reference to atleast some of the figures discussed below, the relative balance ofsympathetic and parasympathetic influences can oscillate on multipletimescales.

While a parabola is shown in FIG. 26 as an example, this may be replacedby a triangle or by any other topologically equivalent shape.

We have discovered a number of specific patterns or shapes occurring inat least some circumictal periods of at least some patients, whichpatterns or shapes may be used as the basis for a state change templateas discussed herein.

Generally, the specific patterns or shapes can be considered asbelonging to one of three categories:

Simple patterns, including the parabola shown in FIG. 26 or the triangleshown in FIG. 27, among others;

Complex patterns, including the notched triangle pattern of FIGS.28A-28C, the “M” pattern of FIGS. 29A-29C, and the “W” pattern of FIG.30, among others;

Polymorphic patterns, containing two or more simple and/or complexpatterns, including fused simple and/or complex patterns, periodic orquasiperiodic oscillations, periodic or quasiperiodic oscillationsoverlaid on a longer term simple and/or complex patterns, and multiplesimple and/or complex patterns, such as those shown in FIGS. 31-38B,among others.

Exemplary patterns or shapes are shown in FIGS. 27-38B. In each of thesefigures, a relevant portion of a graph of a patient's heart rate inbeats per minute (BPM) vs. time in hours from the onset of ECoGmonitoring of his or her seizure activity is shown. Vertical lines markthe electrographic onset and electrographic termination of a seizure.

The reader will have noticed that some patterns notable in FIGS. 27-38Bas being closely correlated in time with a seizure also occur at timeswhen no seizure was detected by ECoG. It should be pointed out thatsince monitoring of brain activity with intracranial electrodes islimited to certain regions, seizures may occur and go undetected if theyoriginate in regions not monitored by the available electrodes. This mayexplain the presence of multiple heart rate patterns in the circumictalperiod when only one seizure was recorded. In other words, the cardiacdata may indicate the occurrence of seizures that intracranialelectrodes failed to detect. The use of cardiac information, such as theuses described and claimed herein, may supplement the inherentlimitations of brain-based seizure detection.

FIG. 27 shows what may be termed a simple pattern, viz., a triangle, inaccordance with an illustrative embodiment of the present disclosure.Herein, when discussing shapes, the words “triangle” and “parabola” canbe used interchangeably. Generally, “triangle” will be used forconvenience only.

FIG. 28A-C shows three graphs of what may be termed a notched triangle.103051 In various examples, the state change template may comprise oneor more shapes that can be considered as comprising a plurality oftriangles. For example, the state change template may comprise one ormore shapes resembling letters of the Latin alphabet.

FIGS. 29A-C shows three graphs of what may be termed an “M” pattern,formed by two contiguous triangles or parabolae. The “A1” pattern may bemonophasic (the heart rate does not drop below the reference value orbaseline) or multiphasic (after raising above the reference value, theheart rate drops below it). An “M” can be considered as distinct from a“notched triangle” in that the indentation of the M generally returnssubstantially to a baseline value and generally divides the M intosubstantially symmetrical halves.

The “M” patterns shown in FIGS. 29A-29C have total durations of about60-90 seconds, beginning anywhere from about 15 seconds beforeelectrographic onset to about 90 seconds after electrographic onset.However, other total durations and beginning times relative toelectrographic onset may occur in other “M” patterns.

FIG. 30 shows a graph of what may be termed a “W” pattern, discerniblefrom about 15 sec after electrographic onset to about 20 seconds afterelectrographic termination. Though not to be bound by theory, the “W”pattern may reflect differences (compared to the “M” pattern) in thetiming of changes in autonomic influences during seizures.

The triangle, notched triangle, “M,” and “W” patterns of FIGS. 27-30 canbe considered to occur on a mesoscopic timescale. However, the samepatterns may be discerned at shorter or longer timescales.

FIGS. 31-38B show patterns that can be considered to occur at longmesoscopic and/or macroscopic timescales. As can be seen and will bediscussed below, the patterns of FIGS. 31-38B can generally beconsidered as polymorphic patterns comprising two or more of the basicshapes, simple patterns, or complex patterns discussed above.

FIG. 31 shows a fused “A1” and “W” pattern. The “W” can be considered asstarting at about 30 seconds before electrographic onset and ending atabout 60-75 seconds after electrographic onset in the region of highestheart rate during the seizure event. The “M” can be considered asstarting a few seconds before electrographic onset and ending about atelectrographic termination. One may also discern a “W” occurring at amicroscopic or short mesoscopic timescale at the notch of the “M.”

Alternatively or in addition, a person of ordinary skill in the art,having the benefit of the present disclosure, may discern an “M”beginning at about 45-60 seconds before electrographic onset and endingat about the middle of the seizure, with a “W” beginning about 30seconds after electrographic onset and ending about 15-30 seconds afterelectrographic termination.

FIGS. 32A-B shows two graphs of patterns of periodic or quasiperiodicoscillations. (For convenience, we will use the term “periodic,”although it must be borne in mind that the frequency and the amplitudeof the oscillations associated with a single seizure in one patient mayvary over the course of about 10 minutes, as shown in FIGS. 32A-B. Inother words, the term “periodic” is not limited herein to refer toseries of oscillations with fixed frequency and amplitude).

The pattern of periodic oscillations may be deformed by a seizure event(e.g., FIG. 32B). In instances where this is not the case, a dysfunctionof the patient's autonomic nervous system may be indicated. For example,FIG. 32A shows a rapid oscillation of the patient's heart rate by asmuch as 40 BPM in a short time.

Detecting a pattern in a preictal period in a time series of heart ratedata may be considered, at least in some patients, as a “prediction” ofa seizure and/or an indication of a period of greater risk of a seizure.Alternatively or in addition, it may be used to aid detection ofseizures originating in brain regions not surveyed by intracranialelectrodes.

Multiple triangles with a certain degree of periodicity and eithermonophasic or biphasic nature can form what may be viewed as a“sawtooth” pattern in the circumictal period. FIG. 33 shows a graph ofanother pattern of periodic oscillations. The periodic oscillations fromabout 15-30 seconds after the seizure to about 3 minutes after theseizure can be considered a sawtooth pattern.

FIGS. 34A-D shows four graphs of patterns of periodic oscillationsoverlaid on a longer-timescale triangle pattern. For example, thepattern in FIG. 34A shows an asymmetric triangle with a trailing slopelasting about 5 minutes, on which is overlaid a pattern of periodicoscillations having an average wavelength of about 20 seconds isdiscernible from about 90 seconds after the seizure until the end of thewindow shown.

FIG. 35 shows, in addition to a pattern of periodic oscillationsoverlaid in the post-ictal period on a longer-timescale trianglepattern, a comb pattern in the preictal period. For a duration of about2.5 minutes starting about 3.5 minutes before electrographic onset, apattern of periodic oscillations is shown with pronounced negativeamplitudes (relative to the average heart rate over the first 30-45seconds of the window) and an average wavelength of about 15 seconds.Again, detecting a pattern in a preictal period in a time series ofheart rate data may be considered, at least in some patients, as a“prediction” of a seizure and/or an indication of a period of greaterrisk of a seizure. Alternatively or additionally, the presence of onepattern of long duration or more than one pattern of any duration in thecircumictal period, are indicative of cardiac or autonomic instability.This information may be used to warn the patient or his caregiver(s) ofan increased risk of a serious outcome and/or institute therapeuticmeasures.

FIG. 36 shows another comb pattern, this one with pronounced positiveamplitudes, overlaid on a longer-timescale parabola.

FIG. 37 shows a triphasic pattern relative to the preictal baseline, inwhich a first positive phase forms a notched triangle from just beforeelectrographic onset until late in the seizure; a second, negative phasefollows until about 30-45 seconds after the seizure; and a third,positive phase ensues with a duration of about 4 min until the end ofthe window.

FIGS. 38A-B shows two graphs from which multiple “M” and/or “W” patternsare discernible in all three of the preictal, ictal, and postictal timeperiods. These multiple “M” and/or “W” patterns can be considered aspart of a macroscopic pattern comprising a plurality of complex shapes.

In addition, very rapid oscillations in heart rate may also occur, andalong with lower frequency oscillations, may provide useful insight intothe behavior of heart rate variability circum-ictally and of itsusefulness for seziure detection, given its differences from thoseobserved outside the circum-ictal period. That is, oscillations at twofrequencies (e.g., slow and fast) or more than two frequencies (e.g.,very fast, slow, and very slow) may overlap to form a pattern that iscommonly associated with a circumictal period.

Any one or more of the patterns shown in FIGS. 27-38B, among others, canbe taken as the basis for a state change template. Also, HRV values canbe derived from the time series of heart rates depicted in FIGS. 27-38B,and one or more distinctive patterns discernible from the HRV values canbe used as the basis for a state change template. Such distinctivepatterns would generally be expected to be distinct from HRV changesresulting from exercise or normal exertion.

Regardless of how HRV values are determined, in one embodiment, thepattern or shape of heart rate variability (as distinct from heart rate)measured at any or all of the timescales (micro-, meso-, or macroscopic)may be used as a template for detection and quantification of statechanges using matched filtering or its autocorrelation function.

In a particular embodiment, the state change template comprises onephase relative to the reference heart rate parameter, three extrema,four directions of heart rate change, and two periods of increased heartrate relative to the reference heart rate parameter. This state changetemplate may be considered to be the “M” pattern shown in FIGS. 29A-29C.

Multiple state change templates, including but not limited to multipletemplates at different timescales, may be used for various purposes. Forexample, a first template found to have a particularly high sensitivity,specificity, or both can be used as a primary detection technique, withother templates used to validate detections made by the first template.For another example, a template found to have high sensitivity but lowspecificity (i.e., giving detections with a relatively high falsepositive rate) can be paired with another template found to have highspecificity to be used in detections with higher sensitivity andspecificity than either alone. For still another example, a firsttemplate can be used to identify a state change e.g., from anon-circumictal state to a preictal state, and this identification canbe used to trigger use of a second template to identify a second statechange, e.g., from a preictal state to an ictal state. For a particularexample, a comb pattern can be used to identify a state change from anon-circumictal state to a preictal state, and an “M” pattern can beused to identify a state change from a preictal state to an ictal state.

In one embodiment, a plurality of matched filters (and/or the output ofone or more of the matched filters as another matched filter or filters)can be used. For example, two or three matched filters, each on aseparate one of the macroscopic, mesoscopic, and microscopic timescalescan be run simultaneously on the time series of heart rate derivativedata. After adequate analysis, comparisons of the results of matchedfiltering at the three times scales can be made to find the matchedfilter/timescale combination(s) giving highest sensitivity, highestspecificity, fastest detection, or two or more thereof. Depending on theintended use, the most useful matched filter/timescale can then be usedand run continuously and its output (detection) used to run the othermatched filters/timescales for detection of changes (at longer orshorter time scales) and validation of detected changes.

Alternatively or in addition to the state change detections discussedherein, circumictal changes at various times scales may be used forassessment of disease state, both among circumictal changes monitoredover long time periods (such as months or years) and between circumictaland non-circumictal states. In one embodiment, such disease stateassessment may include assessment of the patient's risk ofepilepsy-related sudden death (SUDEP).

Regardless of the desired use of circumictal data, circumictal changesmay be quantified in one or more dimensions. In one embodiment, theoutput value of a detection, a disease state assessment, or the like canbe monitored as a function of time (days, month years), bothinter-circumictally and circumictally vs. non-circumictally, with theresults analyzed for the presence of changes and trends. In anotherembodiment, circumictal changes can be classified as a function ofpattern type (e.g., simple, complex, or polymorphic) and their temporalevolution tracked. In another embodiment, the temporal density of thecircumictal period can be defined as percent time spent in a pattern(s).

Quantification of the match between the heart rate derivative shape andthe state change template can also provide information about theduration of a seizure. In one embodiment, the method further comprisesindicating the termination of the state change based upon adetermination that the heart rate derivative shape fails to match thestate change template, after an indication of an occurrence of a statechange.

In one embodiment, the state change template further comprises at leastone second characteristic selected from a magnitude of heart rate changerelative to the reference heart rate parameter, a slope of heart ratechange, a duration of one or more phases, a duration from a heart rateexcursion from the reference heart rate parameter to a peak or a troughheart rate, a total duration of all the phases, or a duration of aconstant slope of heart rate change; and indicating an occurrence of astate change is based upon a determination that the heart rate shapematches a state change template in both the at least one characteristicand in the at least one second characteristic.

The slope can be measured on any time scale, though for cardiac data, itmay be smoother if taken over multiple beats, such as five or fifteenbeats, or over a length of time, such as five to fifteen seconds. Theterm “constant slope” is used herein to refer to a fit, such as aleast-squares fit or other fit, of the data series in question that hasa sufficiently high fit to a straight line as to commend itself to theperson of ordinary skill in the art as being a constant. For example, aregion of a data series having a linear least-squares fit with an R²value of at least 0.9 can be considered to have a constant slope.

As stated above, a state change can be indicated by quantifying thematch of the heart rate shape to the state change template. This statechange indication can be considered as the sole indication of a statechange, it can be validated by other techniques of state changeidentification, or it can be used to verify state changes indicated byother techniques. Such other techniques include those describedelsewhere herein, as well as others known to the person of ordinaryskill in the art or others the subject of one or more patentapplications, such as U.S. patent applications Ser. No. 12/770,562,filed Apr. 29, 2010; Ser. No. 12/771,727, filed Apr. 30, 2010; and Ser.No/ 12/771,783, filed Apr. 30, 2010.

In one embodiment, the determination comprises using a first matchedfilter to yield a first output, building a second matched filter fromthe first output, and using the second matched filter to detect thestate change. In other words, because the passage of a first matchedfilter over a data window will produce a stereotypical output when itbegins passing over a shape which it matches, the stereotypical outputitself can be used to detect a state change prior to, or as a validationof, a detection by the first matched filter.

Thus, in one embodiment, the method further comprises identifying anoccurrence of a state change; and wherein said determining said heartrate derivative shape and said indicating are performed in response tosaid identifying, to validate said identifying.

In another embodiment, the method further comprises identifying anoccurrence of a state change in response to said indicating, to validatesaid indicating. In a further embodiment, the method further comprisesobtaining data relating to at least a portion of a heart beat complexfrom said patient; comparing said at least said portion of said heartbeat complex with a corresponding portion of a reference heart beatcomplex template of said patient, wherein the reference heart beatcomplex template is not indicative of a state change; and validatingsaid indicating an occurrence of a state change, wherein said validatingis based upon a determination that said heart beat complex fails tomatch said reference heart beat complex template.

In one embodiment, the reference heart beat complex template is selectedfrom a normal template (e.g., a reference heart beat complex templatenot indicative of a state change from a patient with healthy heartactivity) or an abnormal template (e.g., a reference heart beat complextemplate not indicative of a state change from a patient with current orpast unhealthy heart activity).

For example, a heart rate derivative shape present over a firsttimescale not typically found in a reference heart rate derivative shapeobserved during rising from lying to sitting, rising from sitting tostanding, minor physical exertion, exercise, or emotionally-intenseexperiences can be used to indirectly validate an identification of aseizure made from a rise in heart rate, or vice versa.

Alternatively or in addition, in another embodiment, the methodcomprises determining a second reference heart rate parameter;determining a second heart rate derivative shape from said time seriesof cardiac data, wherein said second heart rate derivative shapecomprises at least one second characteristic selected from a number ofphases relative to said reference heart rate parameter, a number ofpositive phases relative to said reference heart rate parameter, anumber of negative phases relative to said reference heart rateparameter, a number of extrema of said second heart rate derivative, ora number of directions of change of said second heart rate derivative;and validating said indicating an occurrence of a state change, whereinsaid validating is based upon a determination that said second heartrate derivative shape matches a second state change template in said atleast one second characteristic.

The present disclosure also provides a method for indicating anoccurrence of a state change, comprising obtaining data relating to atleast a portion of a heart beat complex from a patient; comparing the atleast the portion of the heart beat complex with a corresponding portionof a reference heart beat complex template of the patient; andindicating an occurrence of a state change based upon a determinationthat the heart beat complex fails to match the reference heart beatcomplex template.

A heart beat complex is used herein to refer to a PQRST complex, as isknown from the electrocardiography (EKG) art, from a single heart beat,including both the relative and absolute magnitudes of the P-, Q-, R-,S-, and T-waves, and all of the intervals P-Q, P-R, P-S, P-T, Q-R, Q-S,Q-T, R-S, R-T, and S-T. A portion of the heart beat complex is then anyone or more of the relative and/or absolute magnitudes of the waves,their shapes, and/or one or more of the intervals between waves. Arelative magnitude may be defined according to any one or more of thewaves of the complex, e.g., an R-wave amplitude can be defined as rtimes the P-wave amplitude. FIG. 39 shows exemplary heart beat complexeswith P- and R-waves identified by name. The horizontal lines are drawnfor convenience, to point out plausible deviations between the variouswaves of different beat complex.

Although the term “a heart beat complex” is used above, a plurality,such as, but not necessarily, a sequential plurality, of heart beatcomplexes can be used, with the comparing being done for one or more ofthe plurality of heart beat complexes. The plurality may be a fixed setof beats or a moving window over a predetermined time or number ofbeats.

In one embodiment, the portion of the heart beat complex comprises atleast one of an amplitude of a P wave, a polarity of a P wave, at leastone of an amplitude of an R wave, a polarity of a Q wave, a polarity ofan R wave, an amplitude of an S wave, a polarity of an S wave a polarityof an S wave—an amplitude of a T wave, a polarity of a T wave, an areaunder the curve of a P wave, an area under the curve of a Q wave, anarea under the curve of an R wave, an area under the curve of an S wave,an area under the curve of a T wave, a width of a P wave, a with of a Qwave, a width of an n R wave, a width of an S wave, a width of a T wave,a morphology of a P wave, a morphology of a Q wave, a morphology of an Rwave, a morphology of a T wave, a magnitude of a change in the distancefrom a P wave to a Q wave, a magnitude of a change in the distance froma P wave to an R wave, a magnitude of a change in the distance from a Qwave to an R wave. a magnitude of a change in the distance from an Rwave to an S wave, a magnitude of a change in the distance from an Rwave to a T wave, a magnitude of a change in the distance from an S waveto a T wave, a magnitude of an S-T segment elevation, a magnitude of anS-T segment depression, a magnitude of a Q-T segment elevation, amagnitude of a Q-T segment depression, a P-R interval, an R-S interval,an S-T interval, an R-T interval, and a Q-T interval.

The reference heart beat complex template can be derived from anynon-state change heart beats. Such beats may be one, some, or all thesame beats used to define the reference heart rate parameter and/orreference HRV described above, but need not be any of the same beats. Inone embodiment, the reference heart beat complex template comprises atleast one matched filter. In a further embodiment, the heart beatcomplex fails to match the reference heart beat complex template if amatched filter score for the heart beat complex to the at least onematched filter is less than a heart beat complex value threshold.

Although one reference heart beat complex template is referred to above,a plurality of reference heart beat complexes may be used. For example,a plurality of reference heart beat complexes can be used on the sameheart beats, or one or more of the plurality can be used at differenttimes of day, under different states of exertion or arousal, in view ofchanges in heart health histories or differences in heart health betweenpatients, among other possibilities. In one embodiment, a secondreference heart beat complex template comprises at least one of T wavedepression, P-Q segment elongation, another abnormality, or two or morethereof, relative to the canonical “normal” heart beat complex.

Alternatively, one or more heart beat complex templates derived fromheart beat complexes observed during one or more periods of state changemay be used, with a state change declared if the heart beat complex(es)match(es) the state change heart beat complex template(s).

FIG. 40A shows an exemplary heart beat complex derived from datacollected over an entire period of EKG monitoring of a patient, whichmay be used as a reference heart beat complex template. FIG. 40B showsan exemplary heart beat complex derived from EKG data collected from thesame patient during circumictal periods only, which may be used as astate change heart beat complex template.

In the event a plurality of reference heart beat complex templates areused, one or more of the templates may be modified over time, based onobserved changes in the patient's heart beat complexes, such as duringnon-state-change periods.

The at least portion of the heart beat complex and the correspondingportion of the reference heart beat complex template can be comparedusing any of the pattern matching techniques described herein. Becausethe reference heart beat complex template is taken from non-seizureheart beats, a failure to match between the at least portion of theheart beat complex and the corresponding portion of the reference heartbeat complex template is an indirect indication of a seizure.

Quantification of the match between a portion of a heart beat complexand the corresponding portion of the reference heart beat complextemplate can also provide information about the duration of a seizure.In one embodiment, the method further comprises obtaining a time seriesof data relating to a plurality of heart beat complexes from thepatient; comparing at least a portion of each of a sequential pluralityof heart beat complexes with a corresponding portion of the firstreference heart beat complex template; and indicating the termination ofthe state change based upon a determination that at least one heart beatcomplex of the sequential plurality matches the reference heart beatcomplex template, after an indication of an occurrence of a statechange. Matched filters can be used in this determination, as describedelsewhere herein.

In one embodiment, the determination further comprises analyzing one ormore of a pulse shape, an R wave amplitude, an apex cardiogram, or apressure wave, to validate or classify the state change.

In one embodiment, a heart beat complex fails to match a reference heartbeat complex template if a matched filter output for said heart beatcomplex is less than a first matched filter threshold, or differs from asecond matched filter threshold by at least a predetermined magnitude.

Also similarly to the heart rate derivatives described above, a statechange can be indicated by quantifying the match of the portion of theheart beat complex to the reference heart beat complex template. Thisstate change indication can be considered as the sole indication of astate change, it can be validated by other techniques of state changeidentification, or it can be used to verify state changes indicated byother techniques. Such other techniques include those describedelsewhere herein, as well as others known to the person of ordinaryskill in the art or others the subject of one or more patentapplications, such as U.S. patent applications Ser. No. 12/770,562,filed Apr. 29, 2010; Ser. No. 12/771,727, filed Apr. 30, 2010; and Ser.No. 12/771,783, filed Apr. 30, 2010.

Thus, in one embodiment, the method further comprises identifying anoccurrence of a state change; wherein the obtaining, the comparing, andthe indicating are performed in response to the identifying, to validatethe identifying.

Particularly, the prior indicating can be performed using heart rate orHRV data, and in one embodiment, one or more heart beats taken from thereference heart rate parameter of the heart rate or HRV data can be usedto define the reference heart beat complex template and one or moreheart beats taken from the excursion of the heart rate or HRV data fromits reference heart rate parameter can be used to as the heart beatcomplex from which a portion is matched with a corresponding portionfrom the reference heart beat complex template. By “zooming” from theheart rate or HRV shape into one or more individual heart beats givingrise to the heart rate or HRV shape, a state change indication from HRVdata can be validated. For example, if the heart rate or HRV shape givesan indication of a state change, but one or more heart beat complexesfrom the putative state change match the reference heart beat complextemplate, the excursion of heart rate or HRV from the reference heartrate parameter may be considered to result from exercise or anothernon-seizure-event source.

In another embodiment, the method further comprises identifying anoccurrence of a state change in response to said indicating, to validatesaid indicating. For example, identifying an occurrence of a statechange to validate an indication can be performed by using a priordetection algorithm, using a second characteristic of the state changetemplate, or matching at least a portion of a heart beat complex with acorresponding portion from a reference heart beat complex template,among other techniques.

The present disclosure also provides a method for identifying a statechange template from cardiac data, comprising obtaining a time series ofcardiac data from a patient during a first time window; determining atime of occurrence of at least one state change suffered by the patientduring the first time window; and either (i) determining at least onestate change template in the time series of cardiac data within thefirst time window and timewise correlated with the at least one statechange, wherein the at least one state change template comprises atleast one characteristic selected from a number of phases relative to areference heart rate parameter, a number of extrema, a number ofdirections of change, a number of positive phases relative to saidreference heart rate parameter, or a number of negative phases relativeto said reference heart rate parameter, or (ii) determining at least onereference heart beat complex template in the time series of cardiac datawithin the first time window and not timewise correlated with the atleast one state change.

In a particular embodiment, the at least one characteristic comprises atleast one of the amplitude of at least one phase, the duration of atleast one phase, the valence (positive or negative) of at least onephase, at least one slope of at least one phase, the arc length of atleast one phase, the number of extrema in at least one phase, and thesharpness of the extrema of at least one phase.

The cardiac data can comprise one or more of heart rate data, HRV data,or heart beat complex data, such as data from at least a portion of eachof a plurality of heart beat complexes, among others. The cardiac datacan be derived from signals collected from or related to EKG, heartsounds (such as can be collected by a microphone mounted on the skin ofthe chest), blood pressure, apex cardiography, echocardiography,thermography, or blood flow velocities estimated by Doppler imaging,among other techniques known to the person of ordinary skill in the art.

The time of occurrence of the at least one state change can bedetermined by any appropriate technique, such as EEG, cardiac-basedseizure detection (such as that disclosed in U.S. patent applicationsSer. No. 12/770,562, filed Apr. 29, 2010; Ser. No. 12/771,727, filedApr. 30, 2010; and Ser. No. 12/771,783, filed Apr. 30, 2010), testing ofthe patient's responsiveness (such as that disclosed in U.S. patentapplication Ser. No. 12/756,065, filed Apr. 7, 2010, the disclosure ofwhich is hereby incorporated herein by reference), among othertechniques known to the person of ordinary skill in the art or otherwiseavailable.

The finding of a timewise correlation of at least one state changetemplate with a state change, or the finding of a non-timewisecorrelation of at least one reference heart beat complex template with astate change, can be performed by any appropriate technique. “Timewisecorrelation” refers to any substantially repeated duration between aputative template and a state change, and includes putative templatestaking place before a state change, during a state change, or after astate change.

The state change template can be further defined according to at leastone second characteristic selected from a magnitude of cardiac datavalue change relative to the reference heart rate parameter cardiac dataseries, a slope of cardiac data value change, a duration of one or morephases, a duration from a cardiac data excursion from the referenceheart rate parameter cardiac data series to a peak or a trough cardiacdata series, a total duration of a cardiac data excursion from thereference heart rate parameter cardiac data series, or a duration of aconstant slope of cardiac data series change.

In another embodiment, the present disclosure relates to a method fordetermining at least one property of a pattern indicative of anoccurrence of a state change. In one embodiment, this method comprisesobtaining a time series of cardiac data from a patient; determining ifat least one heart rate derivative shape forms at least one pattern; anddetermining at least one property of the pattern.

For example, in one embodiment, the at least one property of the patterncomprises a shape of the pattern, a time of occurrence of the pattern, atime elapsed between occurrences of the pattern, and an association ofthe pattern with a state change of a body organ.

Any state change of any body organ may be considered. In one embodiment,the at least one property of the pattern is an association of thepattern with a state change of the brain. In a further embodiment, thestate change of the brain is an epileptic seizure.

The state change template or reference heart beat complex templateproduced by the present method can be used in a method as describedabove.

However the state change is identified, and regardless of the statechange template, the timescale, and the subperiod of the circumictalperiod in which state changes are detected, in some embodiments, anindication of a state change can be used as the basis for taking aresponsive action selected from warning, logging the time of a statechange, computing and storing one or more state change severity indices,treating the state change, or two or more thereof. In one embodiment,quantification of one or more state change severity indices can beperformed through comparisons of matched filtering outputs, althoughscaling and/or other appropriate transformation may be required when theshapes are similar but their sizes are not.

A state change warning may be given as, for example, a warning tone orlight, vibration, pressure, or scent implemented by a medical device ora device adapted to receive indications of the state change; as anautomated email, text message, telephone call, or video message sentfrom a medical device or a unit in communication with a medical deviceto the patient's cellular telephone, PDA, computer, television, 911 oranother emergency contact number for paramedic/EMT services, etc. Such awarning may allow the patient or his or her caregivers to take measuresprotective of patient's well-being and those of others, e.g., pullingout of traffic and turning off a car, when the patient is driving;stopping the use of machinery, contacting another adult if the patientis providing childcare, removing the patient from a swimming pool orbathtub, lying down or sitting if the patient is standing, etc.

The time may be logged by receiving an indication of the current timeand associating the indication of the current time with an indication ofthe state change.

State change severity indices may be calculated and stored byappropriate techniques and apparatus.

In an exemplary embodiment of the present disclosure, any method ofindicating a seizure can further comprise taking a responsive actionbased upon the identifying the state change. The responsive action mayinclude providing a warning and/or notifying the patient or a caregiver,logging the time of a state change, computing and storing one or morestate change severity indices, or treating the state change.

In one embodiment of the present disclosure, treating the state changecomprises providing a neurostimulation therapy. The neurostimulationtherapy may involve applying an electrical, mechanical, magnetic,electro-magnetic, photonic, acoustic, cognitive, sensori-perceptualand/or chemical signal to a neural structure of the body. The neuralstructure may be a brain, a spinal cord, a peripheral nerve, a cranialnerve, or another neural structure. In a particular embodiment, theresponsive action comprises treating the state change by providing acranial nerve stimulation therapy. Cranial nerve stimulation has beenproposed to treat a number of medical conditions pertaining to ormediated by one or more structures of the nervous system, includingepilepsy, movement disorders, depression, anxiety disorders and otherneuropsychiatric disorders, dementia, traumatic brain injury, coma,migraine headache, obesity, eating disorders, sleep disorders, cardiacdisorders (such as congestive heart failure and atrial fibrillation),hypertension, endocrine disorders (such as diabetes and hypoglycemia),and pain (including neuropathic pain and fibromyalgia), among others.See, e.g., U.S. Pat. Nos. 4,867,164; 5,299,569; 5,269,303; 5,571,150;5,215,086; 5,188,104; 5,263,480; 6,587,719; 6,609,025; 5,335,657;6,622,041; 5,916,239; 5,707,400; 5,231,988; and 5,330,515.

In some embodiments, electrical neurostimulation may be provided byimplanting an electrical device underneath the skin of a patient anddelivering an electrical signal to a nerve such as a cranial nerve. Inanother alternative embodiment, the signal may be generated by anexternal pulse generator outside the patient's body, coupled by an RF orwireless link to an implanted electrode. In one embodiment, thetreatment comprises at least one of applying an electrical signal to aneural structure of a patient; delivering a drug to a patient; orcooling a neural structure of a patient. When the treatment comprisesapplying an electrical signal to a portion of a neural structure of apatient, the neural structure may be at least one of a portion of abrain structure of the patient, a portion of a cranial nerve of apatient, a portion of a spinal cord of a patient, a portion of asympathetic nerve structure of the patient, a portion of aparasympathetic nerve structure of the patient, and/or a portion of aperipheral nerve of the patient.

The above methods can be performed alone. In one embodiment, the abovemethods can be performed in combination with a continuous or open-looptherapy for epilepsy. In one embodiment, the above methods are performedto take action in response to an indication of a state change, and atall or most other times, a chronic therapy signal is applied to a targetstructure in the patient's body. In one embodiment, the target structureis a cranial nerve, such as the vagus nerve.

Although not limited to the following, an exemplary system capable ofimplementing embodiments of the present disclosure is described below.FIG. 22 depicts a stylized implantable medical system (IMD) 2200 forimplementing one or more embodiments of the present disclosure. Anelectrical signal generator 2210 is provided, having a main body 2212comprising a case or shell with a header 2216 for connecting to aninsulated, electrically conductive lead assembly 2222. The generator2210 is implanted in the patient's chest in a pocket or cavity formed bythe implanting surgeon just below the skin (indicated by a dotted line2245), similar to the implantation procedure for a pacemaker pulsegenerator.

A nerve electrode assembly 2225, preferably comprising a plurality ofelectrodes having at least an electrode pair, is conductively connectedto the distal end of the lead assembly 2222, which preferably comprisesa plurality of lead wires (one wire for each electrode). Each electrodein the electrode assembly 2225 may operate independently oralternatively, may operate in conjunction with the other electrodes. Inone embodiment, the electrode assembly 2225 comprises at least a cathodeand an anode. In another embodiment, the electrode assembly comprisesone or more unipolar electrodes.

Lead assembly 2222 is attached at its proximal end to connectors on theheader 2216 of generator 2210. The electrode assembly 2225 may besurgically coupled to the vagus nerve 2227 in the patient's neck or atanother location, e.g., near the patient's diaphragm or at theesophagus/stomach junction. Other (or additional) cranial nerves such asthe trigeminal and/or glossopharyngeal nerves may also be used todeliver the electrical signal in particular alternative embodiments. Inone embodiment, the electrode assembly 2225 comprises a bipolarstimulating electrode pair 2226, 2228 (i.e., a cathode and an anode).Suitable electrode assemblies are available from Cyberonics, Inc.,Houston, Tex., USA as the Model 302 electrode assembly. However, personsof skill in the art will appreciate that many electrode designs could beused in the present disclosure. In one embodiment, the two electrodesare wrapped about the vagus nerve, and the electrode assembly 2225 maybe secured to the vagus nerve 2227 by a spiral anchoring tether 2230such as that disclosed in U.S. Pat. No. 4,979,511, issued Dec. 25, 1990to Reese S. Terry, Jr. Lead assembly 2222 may be secured, whileretaining the ability to flex with movement of the chest and neck, by asuture connection to nearby tissue (not shown).

In alternative embodiments, the electrode assembly 2225 may comprisetemperature sensing elements, blood pressure sensing elements, and/orheart rate sensor elements. Other sensors for other body parameters mayalso be employed. Both passive and active stimulation may be combined ordelivered by a single IMD according to the present disclosure. Either orboth modes may be appropriate to treat a specific patient underobservation.

The electrical pulse generator 2210 may be programmed with an externaldevice (ED) such as computer 2250 using programming software known inthe art. A programming wand 2255 may be coupled to the computer 2250 aspart of the ED to facilitate radio frequency (RF) communication betweenthe computer 2250 and the pulse generator 2210. The programming wand2255 and computer 2250 permit non-invasive communication with thegenerator 2210 after the latter is implanted. In systems where thecomputer 2250 uses one or more channels in the Medical ImplantCommunications Service (MICS) bandwidths, the programming wand 2255 maybe omitted to permit more convenient communication directly between thecomputer 2250 and the pulse generator 2210.

Turning now to FIG. 23A, a block diagram depiction of a medical device2300 is provided, in accordance with one illustrative embodiment of thepresent disclosure.

In some embodiments, the medical device 2300 may be implantable (such asimplantable electrical signal generator 2210 from FIG. 22), while inother embodiments the medical device 2300 may be completely external tothe body of the patient.

The medical device 2300 (such as generator 2210 from FIG. 22) maycomprise a controller 2310 capable of controlling various aspects of theoperation of the medical device 2300. The controller 2310 is capable ofreceiving internal data or external data, and in one embodiment, iscapable of causing a stimulation unit 2320 (FIG. 23B) to generate anddeliver an electrical signal to target tissues of the patient's body fortreating a medical condition. For example, the controller 2310 mayreceive manual instructions from an operator externally, or may causethe electrical signal to be generated and delivered based on internalcalculations and programming. In other embodiments, the medical device2300 does not comprise a stimulation unit 2320 (FIG. 23A). In eitherembodiment, the controller 2310 is capable of affecting substantiallyall functions of the medical device 2300.

The controller 2310 may comprise various components, such as a processor2315, a memory 2317, etc. The processor 2315 may comprise one or moremicrocontrollers, microprocessors, etc., capable of performing variousexecutions of software components. The memory 2317 may comprise variousmemory portions where a number of types of data (e.g., internal data,external data instructions, software codes, status data, diagnosticdata, etc.) may be stored. The memory 2317 may comprise one or more ofrandom access memory (RAM), dynamic random access memory (DRAM),electrically erasable programmable read-only memory (EEPROM), flashmemory, etc.

As stated above, in one embodiment, the medical device 2300 may alsocomprise a stimulation unit 2320 capable of generating and deliveringelectrical signals to one or more electrodes 1326, 1328 via leads 2301(FIG. 23B). A lead assembly such as lead assembly 2222 (FIG. 22) may becoupled to the medical device 2300. Therapy may be delivered to theleads 2301 comprising the lead assembly 2222 by the stimulation unit2320 based upon instructions from the controller 2310. The stimulationunit 2320 may comprise various circuitry, such as electrical signalgenerators, impedance control circuitry to control the impedance “seen”by the leads, and other circuitry that receives instructions relating tothe delivery of the electrical signal to tissue. The stimulation unit2320 is capable of delivering electrical signals over the leads 2301comprising the lead assembly 2222. As should be apparent, in certainembodiments, the medical device 2300 does not comprise a stimulationunit 2320, lead assembly 2222, or leads 2301.

In other embodiments, a lead 2301 is operatively coupled to anelectrode, wherein the electrode is adapted to couple to at least one ofa portion of a brain structure of the patient, a cranial nerve of apatient, a spinal cord of a patient, a sympathetic nerve structure ofthe patient, or a peripheral nerve of the patient.

The medical device 2300 may also comprise a power supply 2330. The powersupply 2330 may comprise a battery, voltage regulators, capacitors,etc., to provide power for the operation of the medical device 2300,including delivering the therapeutic electrical signal. The power supply2330 comprises a power source that in some embodiments may berechargeable. In other embodiments, a non-rechargeable power source maybe used. The power supply 2330 provides power for the operation of themedical device 2300, including electronic operations and the electricalsignal generation and delivery functions. The power supply 2330 maycomprise a lithium/thionyl chloride cell or a lithium/carbonmonofluoride (LiCFx) cell if the medical device 2300 is implantable, ormay comprise conventional watch or 9V batteries for external (i.e.,non-implantable) embodiments. Other battery types known in the art ofmedical devices may also be used.

The medical device 2300 may also comprise a communication unit 2360capable of facilitating communications between the medical device 2300and various devices. In particular, the communication unit 2360 iscapable of providing transmission and reception of electronic signals toand from a monitoring unit 2370, such as a handheld computer or PDA thatcan communicate with the medical device 2300 wirelessly or by cable. Thecommunication unit 2360 may include hardware, software, firmware, or anycombination thereof.

The medical device 2300 may also comprise one or more sensor(s) 2312coupled via sensor lead(s) 2311 to the medical device 2300. Thesensor(s) 2312 are capable of receiving signals related to aphysiological parameter, such as the patient's heart beat, bloodpressure, and/or temperature, and delivering the signals to the medicaldevice 2300. In one embodiment, the sensor(s) 2312 may be the same asimplanted electrode(s) 2226, 2228 (FIG. 22). In other embodiments, thesensor(s) 2312 are external structures that may be placed on thepatient's skin, such as over the patient's heart or elsewhere on thepatient's torso.

In one embodiment, the medical device 2300 may comprise a cardiac datacollection module 2365 that is capable of collecting cardiac datacomprising fiducial time markers of each of a plurality of heart beats.The cardiac data collection module 2365 may also process or conditionthe cardiac data. The cardiac data may be provided by the sensor(s)2312. The cardiac data collection module 2365 may be capable ofperforming any necessary or suitable amplifying, filtering, andperforming analog-to-digital (A/D) conversions to prepare the signalsfor downstream processing. The cardiac data collection module, in oneembodiment, may comprise software module(s) that are capable ofperforming various interface functions, filtering functions, etc., toprocess fiducial time markers of each of a plurality of heart beats. Inanother embodiment the cardiac data collection module 2365 may comprisehardware circuitry that is capable of performing these functions. In yetanother embodiment, the cardiac data collection module 2365 may comprisehardware, firmware, software and/or any combination thereof. A moredetailed illustration of the cardiac data collection module 2365 isprovided in FIG. 24A and accompanying description below.

The cardiac data collection module 2365 is capable of collecting cardiacdata comprising fiducial time markers of each of a plurality ofcandidate heart beats and providing the collected cardiac data to aheart beat/interval determination module 2375. Based upon the signalsprocessed by the cardiac data collection module 2365, the heartbeat/interval determination module 2375 may calculate an interbeatinterval from a consecutive pair of the fiducial time markers and storesuch interbeat interval or forward it on for furtherprocessing/analysis. The heart beat/interval determination module 2375may comprise software module(s) that are capable of performing variousinterface functions, filtering functions, etc., to calculate interbeatintervals. In another embodiment the heart beat/interval determinationmodule 2375 may comprise hardware circuitry that is capable ofperforming these functions. In yet another embodiment, the heartbeat/interval determination module 2375 may comprise hardware, firmware,software and/or any combination thereof. Further description of theheart beat/interval determination module 2375 is provided in FIG. 24Band accompanying description below.

The heart beat/interval determination module 2375 is capable ofcalculating an interbeat interval and providing the interbeat intervalto the heart rate/heart rate variability (HRV)/complex module 2397.Based upon one or more interbeat intervals received from the heartbeat/interval determination module 2375, and/or signals of sufficientsampling rate to provide information regarding the heart beat complexreceived from the cardiac data collection module 2365, the HRderivative/complex module 2397 determines at least one or more of anheart rate (such as from an interbeat interval determined from aconsecutive pair of fiducial time markers), a heart rate variability(such as from two consecutive interbeat intervals determined fromfiducial time markers), or at least a portion of a heart beat complex.

The HR derivative/complex module 2397 may comprise software module(s)that are capable of performing various interface functions, filteringfunctions, etc., to calculate the various values. In another embodimentthe HR derivative/complex module 2397 may comprise hardware circuitrythat is capable of performing these functions. In yet anotherembodiment, the HR derivative/complex module 2397 may comprise hardware,firmware, software and/or any combination thereof. Further descriptionof the HR derivative/complex module 2397 is provided in FIG. 24E andaccompanying description below.

The HR derivative/complex module 2397 is capable of forwarding thecalculated information to template match module 2399. Based upon theinformation received by the template match module 2399, it performs anyoperations desired to indicate a state change. For example, the templatematch module 2399 may indicate a state change based on one or more of aheart rate shape matching an appropriate state change template, an HRVshape matching an appropriate state change template, a portion or moreof a heart beat complex failing to match a reference heart beat complextemplate, or two or more of the foregoing. The template match module2399 may comprise software module(s) that are capable of performingvarious interface functions, filtering functions, etc., to indicate astate change. In another embodiment the template match module 2399 maycomprise hardware circuitry that is capable of performing thesefunctions. In yet another embodiment, the template match module 2399 maycomprise hardware, firmware, software and/or any combination thereof.Further description of the template match module 2399 is provided inFIG. 24F and accompanying description below.

In addition to components of the medical device 2300 described above, animplantable medical system may comprise a storage unit to store anindication of at least one of state change or an increased risk of astate change. The storage unit may be the memory 2317 of the medicaldevice 2300, another storage unit of the medical device 2300, or anexternal database, such as the local database unit 2355 or a remotedatabase unit 2350. The medical device 2300 may communicate theindication via the communications unit 2360. Alternatively or inaddition to an external database, the medical device 2300 may be adaptedto communicate the indication to at least one of a patient, a caregiver,or a healthcare provider.

In various embodiments, one or more of the units or modules describedabove may be located in a monitoring unit 2370 or a remote device 2392,with communications between that unit or module and a unit or modulelocated in the medical device 2300 taking place via communication unit2360. For example, in one embodiment, one or more of the cardiac datacollection module 2365, the heart beat/interval determination module2375, the HR derivative/complex module 2397, or the template matchmodule 2399 may be external to the medical device 2300, e.g., in amonitoring unit 2370. Locating one or more of the cardiac datacollection module 2365, the heart beat/interval determination module2375, the HR derivative/complex module 2397, or the template matchmodule 2399 outside the medical device 2300 may be advantageous if thecalculation(s) is/are computationally intensive, in order to reduceenergy expenditure and heat generation in the medical device 2300 or toexpedite calculation.

The monitoring unit 2370 may be a device that is capable of transmittingand receiving data to and from the medical device 2300. In oneembodiment, the monitoring unit 2370 is a computer system capable ofexecuting a data-acquisition program. The monitoring unit 2370 may becontrolled by a healthcare provider, such as a physician, at a basestation in, for example, a doctor's office. In alternative embodiments,the monitoring unit 2370 may be controlled by a patient in a systemproviding less interactive communication with the medical device 2300than another monitoring unit 2370 controlled by a healthcare provider.Whether controlled by the patient or by a healthcare provider, themonitoring unit 2370 may be a computer, preferably a handheld computeror PDA, but may alternatively comprise any other device that is capableof electronic communications and programming, e.g., hand-held computersystem, a PC computer system, a laptop computer system, a server, apersonal digital assistant (PDA), an Apple-based computer system, acellular telephone, etc. The monitoring unit 2370 may download variousparameters and program software into the medical device 2300 forprogramming the operation of the medical device, and may also receiveand upload various status conditions and other data from the medicaldevice 2300. Communications between the monitoring unit 2370 and thecommunication unit 2360 in the medical device 2300 may occur via awireless or other type of communication, represented generally by line2377 in FIG. 23. This may occur using, e.g., wand 2255 (FIG. 22) tocommunicate by RF energy with an implantable signal generator 2210.Alternatively, the wand may be omitted in some systems, e.g., systems inwhich the MD 2300 is non-implantable, or implantable systems in whichmonitoring unit 2370 and MD 2300 operate in the MICS bandwidths.

In one embodiment, the monitoring unit 2370 may comprise a localdatabase unit 2355. Optionally or alternatively, the monitoring unit2370 may also be coupled to a database unit 2350, which may be separatefrom monitoring unit 2370 (e.g., a centralized database wirelesslylinked to a handheld monitoring unit 2370). The database unit 2350and/or the local database unit 2355 are capable of storing variouspatient data. These data may comprise patient parameter data acquiredfrom a patient's body, therapy parameter data, state change severitydata, and/or therapeutic efficacy data. The database unit 2350 and/orthe local database unit 2355 may comprise data for a plurality ofpatients, and may be organized and stored in a variety of manners, suchas in date format, severity of disease format, etc. The database unit2350 and/or the local database unit 2355 may be relational databases inone embodiment. A physician may perform various patient managementfunctions (e.g., programming parameters for a responsive therapy and/orsetting thresholds for one or more detection parameters) using themonitoring unit 2370, which may include obtaining and/or analyzing datafrom the medical device 2300 and/or data from the database unit 2350and/or the local database unit 2355. The database unit 2350 and/or thelocal database unit 2355 may store various patient data.

One or more of the blocks illustrated in the block diagram of themedical device 2300 in FIG. 23A or FIG. 23B, may comprise hardwareunits, software units, firmware units, or any combination thereof.Additionally, one or more blocks illustrated in FIG. 23A-B may becombined with other blocks, which may represent circuit hardware units,software algorithms, etc. Additionally, any number of the circuitry orsoftware units associated with the various blocks illustrated in FIG.23A-B may be combined into a programmable device, such as a fieldprogrammable gate array, an ASIC device, etc.

Turning now to FIG. 24A, a more detailed stylized depiction of thecardiac data collection module 2365 of FIG. 23, in accordance with oneillustrative embodiment of the present disclosure is depicted. In oneembodiment, the cardiac data collection module 2365 comprises a cardiacdata signal receiver 2410, an analog-to-digital converter (A/DConverter) 2420, and a cardiac data forwarding unit 2425. The cardiacdata signal receiver 2410 is capable of receiving the signals from thesensor(s) 2312 via receiver circuit 2412. The signal that is received bythe receiver circuit 2412 is processed and filtered to enable the datato be further analyzed and/or processed for determining cardiac data,such as that described above.

The cardiac data signal receiver 2410 may comprise amplifier(s) 2414 andfilter(s) 2416. The amplifiers 2414 are capable of buffering andamplifying the input signals received by the receiver circuit 2412. Inmany cases, the heart beat signal may be attenuated and may becharacterized by significantly low amplitude responses and signal noise.The amplifier(s) 2414 are capable of buffering (amplification by unity)and amplifying the signals for further processing. In one embodiment,the amplifier 2414 may comprise op amp circuit(s), digital amplifier(s),buffer amplifiers, and/or the like.

The cardiac data signal receiver 2410 may also comprise one or morefilters 2416. The filters 2416 may comprise analog filter(s), digitalfilter(s), filters implemented by digital signal processing (DSP) meansor methods, etc. The amplified and buffered signal may be filtered toremove various noise signals residing on the signal. The filter 2416,for example, is capable of filtering out various noise signals caused byexternal magnetic fields, electrical fields, noise resulting fromphysiological activity, etc. Signal noise due to breathing or othersignals produced by the patient's body may be filtered.

The cardiac data signal receiver 2410 provides amplified, filteredsignals to the A/D converter 2420. The A/D converter 2420 performs ananalog-to-digital conversion for further processing. The A/D converter2420 may be one type of a plurality of converter types with variousaccuracies, such as an 8-bit converter, a 12-bit converter, a 24-bitconverter, a 32-bit converter, a 64-bit converter, a 128-bit converter,a 256-bit converter, etc. The converted digital signal is then providedto a cardiac data forwarding unit 2425. In an alternative embodiment,the A/D conversion may be performed prior to filtering or signalprocessing of the heart beat signal. The converted digital signal isthen provided to a cardiac data forwarding unit 2425.

The cardiac data forwarding unit 2425 is capable of organizing,correlating, stacking, and otherwise processing the digitized, buffered,and filtered cardiac data and forwarding it to the heart beat/intervaldetermination module 2375, and/or directly to the HR derivative/complexmodule 2397.

Turning now to FIG. 24B, a more detailed stylized depiction of the heartbeat/interval determination module 2375 of FIG. 23, in accordance withone illustrative embodiment of the present disclosure, is depicted. Theheart beat/interval determination module 2375 may comprise a cardiacdata receiving module 2430, for receiving a time stamp sequence ofcandidate heart beats, a heart beat/interval determination module 2440,and a heart beat/interval time series storage unit 2450. The heartbeat/interval determination module 2375 may determine interbeatintervals for adjacent candidate heart beats as they appear in the timeseries of signals via the cardiac data receiving module 2430. Forexample, cardiac data receiving module 2430 may characterize certaindata points in the time series of signals as being fiducial time markerscorresponding to the start, the peak, or the end of an R-wave of apatient's cardiac cycle.

Once fiducial time markers are determined from the time series ofsignals, the heart beat/interval determination module 2440 may determinethe interval between consecutive beats (“interbeat interval”) andforward this information to heart beat/interval time series storage2450, which may store one or both of a time stamp series associated withfiducial markers indicating of an individual heart beat and a time stampseries of adjacent interbeat intervals. In some embodiments, the heartbeat/interval determination module 2440 may calculate a heart rate,heart rate variability (HRV), or at least a portion of a heart beatcomplex. In other embodiments, heart beat/interval determination module2440 may calculate a heart rate, heart rate variability (HRV), or both.

Turning now to FIG. 24C, a more detailed stylized depiction of the HRderivative/complex module 2397 of FIG. 23, in accordance with oneillustrative embodiment of the present disclosure, is depicted. In oneembodiment, the HR derivative/complex module 2397 may receive variouscardiac data indicative from the cardiac data collection module 2365 orthe heart beat/interval determination module 2375. In the embodimentdepicted in FIG. 24C, the HR derivative/complex module 2397 comprisesunits that perform various calculations, for example, a heart ratecalculation unit 2469 may determine a heart rate from some or allinterbeat intervals and/or pairs of heart beats collected and/oridentified by modules 2365 or 2375. Certain embodiments of thedisclosure may also include a heart rate variability unit 2471 whichdetermines an HRV value from some or all interbeat intervals and/orpairs of heart beats collected and/or identified by modules 2365 or2375, and/or a heart beat complex unit 2472 which analyzes one or moreportions of a heart beat complex, e.g., relative R-wave and P-waveamplitudes, P-wave to R-wave temporal separations, or the like. Ofcourse, one or more of units 2469, 2471, and 2472 may be omitted, ifdesired.

The HR derivative/complex module 2397 need not perform all steps2469-2472. Any steps the HR derivative/complex module 2397 performs maybe in any order, not necessarily that shown.

Although the heart rate calculation unit 2469, the heart ratevariability unit 2471, and the heart beat complex unit 2472 are shown inFIG. 24C as components of HR derivative/complex module 2397, in variousother embodiments, one or more of these units can be included in othermodules.

Turning now to FIG. 24D, a more detailed stylized depiction of thetemplate match module 2399 of FIG. 23, in accordance with oneillustrative embodiment of the present disclosure, is depicted. Thetemplate match module 2399 may receive various data from the HRderivative/complex module 2397, including, for example, one or more aheart rate shape characteristics, one or more HRV shape characteristics,information regarding one or more portions of a heart beat complex, etc.Based upon data from the HR derivative/complex module 2397, the templatematch module 2399 is capable of indicating a state change, such asdescribed above.

In the exemplary depiction shown in FIG. 24D, data received from the HRderivative/complex module 2397 is forwarded to a template comparisonunit 2487, which determines whether one or more of the heart rate shape,HRV shape, or portion of the heart beat complex matches a relevanttemplate. The determination of a match can be performed by knownmathematical techniques, such as matched filtering, or the like. Asignal indicative of the occurrence of a state change is provided bystate change indication unit 2489 if the template comparison isindicative of a state change, such as a seizure.

If a state change is identified by template match module 2399, in oneembodiment, a response may be implemented, such as those described byU.S. patent applications Ser. No. 12/770,562, filed Apr. 29, 2010; Ser.No. 12/771,727, filed Apr. 30, 2010; and Ser. No. 12/771,783, filed Apr.30, 2010.

Turning now to FIG. 25, a stylized flowchart depiction of detecting oneparticular type of state change, namely, a seizure, in accordance withone illustrative embodiment of the present disclosure, is provided. Themedical device 2300 receives a cardiac signal (block 2510). In specificembodiments, the cardiac data collection module 2365 (FIGS. 23 and 24A)of the medical device 2300 receives the cardiac signal. After performingbuffering, amplification, filtering, and A/D conversion of the cardiacsignal, the heart beat/interval determination module 2375 and/or HRderivative/complex module 2397 processes the heart beat signal to deriveHR derivative shapes or heart beat complex morphology (block 2520). Fromthe derived shapes or characteristics, it is decided from one or moretemplate matching operations if a state change is indicated (block2530). This decision may be performed by template match module 2399.

Based upon the decision (block 2530), if no state change is indicated,the medical device 2300 continues to receive the heart beat signal(block 2550, returning flow to block 2510).

However, if a state change is indicated in block 2530, the medicaldevice 2300 or an external unit 2370 may provide an indication of thestate change occurrence and/or take a responsive action (block 2560),such as providing a warning to the patient or his or her caregivers,physician, etc. (block 2575); logging a time of state change (block2577); computing and optionally logging one or more state changeseverity indices (block 2579); and/or providing treatment of the statechange (block 2581). More details on logging, warning, computing seizureseverity, and providing treatment are provided in U.S. patentapplications Ser. No. 12/770,562, filed Apr. 29, 2010; Ser. No.12/771,727, filed Apr. 30, 2010; Ser. No. 12/771,783, filed Apr. 30,2010; and Ser. No. 12/756,065, filed Apr. 7, 2010.

The above methods may be performed by a computer readable programstorage device encoded with instructions that, when executed by acomputer, perform the method described herein.

All of the methods and apparatuses disclosed and claimed herein may bemade and executed without undue experimentation in light of the presentdisclosure. While the methods and apparatus of this disclosure have beendescribed in terms of particular embodiments, it will be apparent tothose skilled in the art that variations may be applied to the methodsand apparatus and in the steps, or in the sequence of steps, of themethod described herein without departing from the concept, spirit, andscope of the disclosure, as defined by the appended claims. It should beespecially apparent that the principles of the disclosure may be appliedto selected cranial nerves other than, or in addition to, the vagusnerve to achieve particular results in treating patients havingepilepsy, depression, or other medical conditions.

In various embodiments, the present disclosure relates to the subjectmatter of the following numbered paragraphs:

34. A method for identifying a state change template from cardiac data,comprising:

obtaining a time series of cardiac data from a patient during a firsttime window;

determining a time of occurrence of at least one state change sufferedby said patient during said first time window; and

either

(i) determining at least one state change template in the time series ofcardiac data within the first time window and timewise correlated withthe at least one state change, wherein the at least one state changetemplate comprises at least one characteristic selected from a number ofphases relative to a reference heart rate parameter, a number ofextrema, area under the curve of at least one phase, a number ofdirections of change, a number of positive phases relative to saidreference heart rate parameter, or a number of negative phases relativeto said reference heart rate parameter, or

(ii) determining at least one reference heart beat complex template insaid time series of cardiac data within said first time window and nottimewise correlated with said at least one state change.

35. The method of number 34, wherein said cardiac data comprises heartrate data, heart rate variability data, or heart rate volatility data.

36. The method of number 34, wherein said cardiac data comprises atleast a portion of each of a plurality of heart beat complexes.

37. The method of number 34, wherein said at least one characteristiccomprises at least one of the amplitude of at least one phase, theduration of at least one phase, the valence (positive or negative) of atleast one phase, the area under the curve of at least one phase, atleast one slope of at least one phase, the arc length of at least onephase, the number of extrema in at least one phase, and the sharpness ofthe extrema of at least one phase.

38. A method for obtaining a state change template indicative of anoccurrence of a state change of interest, comprising:

obtaining a first time series of cardiac data from a patient, the firsttime series not associated with said state change of interest;

determining at least one reference heart rate parameter from said firsttime series of cardiac data;

obtaining a second time series of cardiac data from said patient, thesecond time series being associated with said state change of interest;

determining at least one property of said heart rate derivative, saidproperty comprising at least one of a number of phases relative to saidreference heart rate parameter, the perimeter of at least one phase, anumber of extrema of said heart rate derivative, the sharpness of saidextrema, a number of directions of change of said heart rate derivative,an area under the curve of at least one phase, a number of positivephases, or a number of negative phases; and

determining that the at least one property of said heart rate derivativeof the state of interest is different from the same at least oneproperty of the heart rate derivative not associated with the state ofinterest

obtaining a state change template associated with said state change ofinterest and comprising said at least one property, from said heart ratederivative and using it as a matched filter to detect said state change.

39. The method of number 38, wherein the at least one property of saidpattern comprises a shape of said pattern, a time of occurrence of saidpattern, a time elapsed between occurrences of said pattern, and anassociation of said pattern with a state change of a body organ.

40. The method of number 39, wherein said at least one property of saidpattern is an association of said pattern with a state change of thebrain.

41. The method of number 40, wherein said state change of the brain is aepileptic seizure.

42. The method of number 38, wherein said heart rate derivative is heartrate.

43. The method of number 38, wherein said heart rate derivative is heartrate variability or heart rate volatility.

44. A method for indicating an occurrence of a state change, comprising:

providing a first template comprising at least one of a microscopicstate change template, a mesoscopic state change template, and amacroscopic state change template;

obtaining a time series of cardiac data from a patient;

determining a first cardiac data derivative shape from said time seriesof cardiac data; and,

indicating an occurrence of a state change based upon a determinationthat said first cardiac data derivative shape matches said firsttemplate.

45. The method of number 44, further comprising:

providing a second template comprising at least one of said microscopicstate change template, said mesoscopic state change template, and saidmacroscopic state change template, wherein said second template is notbased upon a state change template included in said first template;

determining a second cardiac data derivative shape from said time seriesof cardiac data;

and wherein said indicating is based upon a determination that saidfirst cardiac data derivative shape matches said first template and saidsecond cardiac data derivative shape matches said second template.

46. The method of number 44, wherein said determination comprises usinga matched filter on a moving window of said first cardiac dataderivative, calculating a time series of outputs of said matched filter,and declaring said match if said time series of outputs is substantiallyequal to a time series of expected output values.

101. A method for indicating an occurrence of a state change,comprising:

obtaining a time series of cardiac data from a patient;

selecting at least one parameter from said cardiac data time series;

determining the magnitude, duration, direction and rate of change ofsaid parameter during a reference state wherein said parameter comprisesat least one of a heart rate, a heart rate variability, a heart ratevolatility, a characteristic of the heart's electrical beat, acharacteristic of the heart's beat sounds, a characteristic of theheart's beat contractility and a characteristic of the heart's beatgenerated pressure;

indicating the occurrence of a state change when at least one of saidvalues is greater or lower than at least one reference state parametervalue, e.g., for a certain time period.

102. The method of number 101 wherein the parameters' values are treatedas phases and extrema endowed with shape, curvature, arc length andinflection points;

indicating the occurrence of a state change when at least one of theparameters' values is greater or lower than at least one reference stateparameter values, e.g., for a certain time period.

103. The method of number 101 wherein the cardiac data parameter'svalue's temporal scale is macroscopic.

104. The method of number 101 wherein the cardiac data parameter'svalue's temporal scale is mesoscopic.

105. The method of number 101 wherein the cardiac data parameter'svalue's temporal scale is microscopic.

106. A method for indicating an occurrence of a state change,comprising:

obtaining a time series of cardiac data from a patient during areference state;

selecting at least one parameter from said cardiac data during saidreference state wherein said reference parameter comprises at least oneof a heart rate, a heart rate variability, a heart rate volatility, acharacteristic of the heart's electrical beat, a characteristic of theheart's beat sounds, a characteristic of the heart's beat contractilityand a characteristic of the heart's beat generated pressure;

constructing a reference template using said at least one referenceparameter value and using said template as a reference matched filter;

indicating an occurrence of a state change based upon a determinationthat the output of said at least one reference matched filter reaches avalue outside the range of values characteristic of the reference state.

107. The method of number 106 wherein the reference matched filter'sscale is macroscopic.

108. The method of number 106 wherein the reference matched filter'sscale is mesoscopic.

109. The method of number 106 wherein the reference matched filter'sscale is microscopic.

110. A method for indicating an occurrence of a state change,comprising:

obtaining a time series of cardiac data from a patient during anon-reference state;

selecting at least one parameter from said cardiac data during saidnon-reference state wherein said non-reference parameter comprises atleast one of a heart rate, a heart rate variability, a heart ratevolatility, a characteristic of the heart's electrical beat, acharacteristic of the heart's beat sounds, a characteristic of theheart's beat contractility and a characteristic of the heart's beatgenerated pressure;

constructing a non-reference template using said at least onenon-reference parameter value and using said non-reference template as anon-reference matched filter;

indicating an occurrence of a state change based upon a determinationthat the output of said at least one non-reference matched filterreaches a value characteristic of the non-reference state values.

111. The method of number 110, wherein the non-reference matchedfilter's scale is macroscopic.

112. The method of number 110, wherein the non-reference matchedfilter's scale is mesoscopic.

113. The method of number 110, wherein the non-reference matchedfilter's scale is microscopic.

114. A method for indicating an occurrence of a state change,comprising:

obtaining a time series of cardiac data from a patient;

selecting at least one reference parameter and at least onenon-reference parameter from said cardiac data wherein said parameterscomprise at least one of a heart rate, a heart rate variability, a heartrate volatility, a characteristic of the heart's electrical beat, acharacteristic of the heart's beat sounds, a characteristic of theheart's beat contractility and a characteristic of the heart's beatgenerated pressure;

constructing a reference template using said at least one referenceparameter value and using said reference template as a reference matchedfilter;

constructing a non-reference template using said at least onenon-reference parameter value and using said non-reference template as anon-reference matched filter;

indicating an occurrence of a state change based upon a determinationthat the output of said at least one reference matched filter reaches avalue outside the values characteristic of the reference state valuesand the output of said at least one non-reference matched filter reachesa value characteristic of the non-reference state values.

115. The method of number 114, wherein the scales of the reference andof the non-reference matched filters are macroscopic.

116. The method of number 114, wherein the scales of the reference andof the non-reference matched filters are mesoscopic.

117. The method of number 114, wherein the scales of the reference andof the non-reference matched filters are microscopic.

118. A method for obtaining a state change template indicative of anoccurrence of a state change of interest, comprising:

obtaining a first time series of cardiac data from a patient, the firsttime series not associated with said state change of interest;

determining at least one parameter from said first time series ofcardiac data wherein said parameters comprise at least one of a heartrate, a heart rate variability, a heart rate volatility, acharacteristic of the heart's electrical beat, a characteristic of theheart's beat sounds, a characteristic of the heart's beat contractilityand a characteristic of the heart's beat generated pressure;

obtaining a second time series of cardiac data from said patient, thesecond time series being associated with said state change of interest;

determining at least one parameter from said second time series ofcardiac data wherein said parameters comprise at least one of a heartrate, a heart rate variability, a heart rate volatility, acharacteristic of the heart's electrical beat, a characteristic of theheart's beat sounds, a characteristic of the heart's beat contractilityand a characteristic of the heart's beat generated pressure;

determining that the at least one parameter from said second time seriesof cardiac data associated with a state change of interest is differentfrom the same at least one parameter of the first time series of cardiacdata not associated with a state change of interest;

obtaining a state change template associated with said state change ofinterest and comprising said at least one property;

using said state change template as a matched filter to detect similarstate changes.

119. The method of number 118, wherein the scale of said template andmatched filter associated with a state change of interest ismacroscopic.

120. The method of number 118, wherein the scale of said template andmatched filter associated with a state change of interest is mesoscopic.

121. The method of number 118, wherein the scale of said template andmatched filter associated with a state change of interest ismicroscopic.

The particular embodiments disclosed above are illustrative only as thedisclosure may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Furthermore, no limitations are intended to thedetails of construction or design herein shown other than as describedin the claims below. It is, therefore, evident that the particularembodiments disclosed above may be altered or modified and all suchvariations are considered within the scope and spirit of the disclosure.Accordingly, the protection sought herein is as set forth in the claimsbelow.

What is claimed:
 1. A method of treating a medical condition in apatient using an implantable medical device, the implantable medicaldevice including a first electrode coupled to a first cranial nervestructure and a second electrode coupled to a second cranial nervestructure, where the first cranial nerve structure is a left portion ofa cranial nerve and the second cranial nerve structure is a rightportion of the cranial nerve, the method comprising: obtaining datarelating to at least a portion of a heart beat complex from a patient;comparing the at least the portion of the heart beat complex with acorresponding portion of a first reference heart beat complex templateof the patient; indicating an occurrence of a state change based upon adetermination that the heart beat complex fails to match the firstreference heart beat complex template; providing a first electricalsignal to the first cranial nerve structure of the patient using a firstpolarity configuration in which the first electrode functions as acathode and the second electrode functions as an anode, the firstelectrical signal is configured to induce action potentials in the firstcranial nerve structure, wherein a charge accumulates at the anode andthe cathode as a result of the first electrical signal; switching fromthe first polarity configuration to a second polarity configuration upontermination of the first electrical signal where the first electrodefunctions as the anode and the second electrode functions as the cathodein the second polarity configuration; and providing a second electricalsignal to the second cranial nerve structure in the second polarityconfiguration, the second electrical signal is configured to induceaction potentials in the second cranial nerve structure where at least aportion of the second electrical signal comprises the accumulated chargefrom the first electrical signal.
 2. The method of claim 1, furthercomprising verifying the occurrence of the seizure based upon thecomparison.
 3. The method of claim 1, wherein the verification of theoccurrence of the seizure is based on a determination that the portionof the heart beat complex shape failed to match the correspondingportion of the reference heart beat complex shape template.
 4. Themethod of claim 3, wherein the identifying further includes: determininga second reference heart rate derived shape from the time series ofcardiac data where the second reference heart rate derived shapecomprises a second characteristic selected from a second number ofphases relative to the second reference heart rate derived shape; asecond number of positive phases relative to the second reference heartrate derived shape; a second number of negative phases relative to thesecond reference heart rate derived shape; a second number of extrema ofthe second heart rate derivative; a second area under a second curve ofa second phase; or a second number of directions of change of the secondheart rate derivative.
 5. The method of claim 4, wherein the identifyingthe occurrence of the seizure is further based upon a determination thatthe second reference heart rate derived shape matches a second seizuretemplate in the second characteristic.
 6. The method of claim 3, whereinthe heart rate derivative is at least one of a heart rate and a heartrate variability.
 7. The method of claim 1, wherein the identifyingfurther includes: obtaining a time series of cardiac data from thepatient; determining a reference heart rate derived shape from the timeseries of cardiac data where the reference heart rate derived shapecomprises at least one characteristic selected from: a number of phasesrelative to the reference heart rate parameter; a number of extrema of aheart rate derivative; a number of directions of change of the heartrate derivative; an area under a first curve of a first phase; a numberof positive phases; or a number of negative phases.
 8. The method ofclaim 1, wherein the portion of the heart beat complex shape comprisesat least one of: an amplitude of a P wave; a polarity of the P wave; anamplitude of an R wave; a polarity of a Q wave; a polarity of the Rwave; an amplitude of an S wave; a polarity of the S wave; an amplitudeof a T wave; a polarity of the T wave; an area under a curve of the Pwave; an area under a curve of the Q wave; an area under a curve of theR wave; an area under a curve of the S wave; an area under a curve ofthe T wave; a width of the P wave; a width of the Q wave; a width of theR wave; a width of the S wave; a width of the T wave; a morphology ofthe P wave; a morphology of the Q wave; a morphology of the R wave; amorphology of the T wave; a magnitude of a change in a distance from theP wave to the Q wave; a magnitude of a change in a distance from the Pwave to the R wave; a magnitude of a change in a distance from the Qwave to the R wave; a magnitude of a change in a distance from the Rwave to the S wave; a magnitude of a change in a distance from the Rwave to the T wave; a magnitude of a change in a distance from the Swave to the T wave; a magnitude of an S-T segment elevation; a magnitudeof an S-T segment depression; a magnitude of a Q-T segment elevation; amagnitude of a Q-T segment depression; a P-R interval; an R-S interval;an S-T interval; an R-T interval; and a Q-T interval.
 9. The method ofclaim 1, wherein the comparing further comprises comparing the portionof the heart beat complex shape with a corresponding portion of a secondreference heart beat complex shape template of the patient, and whereinthe verification is based upon a determination that the heart beatcomplex shape fails to match at least one of the reference heart beatcomplex shape template and the second reference heart beat complex shapetemplate.
 10. The method of claim 1, wherein the identifying theoccurrence of the seizure is based upon a determination that a heartrate derived shape matches a seizure template in at least onecharacteristic.
 11. The method of claim 1, wherein the comparing furthercomprises obtaining a corresponding portion of a second reference heartbeat complex shape template of the patient and comparing the portion ofthe reference heart beat complex shape with the corresponding portion ofa second reference heart beat complex shape template of the patient, andwherein the verification is based upon a determination that the heartbeat complex shape fails to match both the reference heart beat complexshape template and the second reference heart beat complex shapetemplate.
 12. The method of claim 1, further comprising obtaining asecond reference heart beat complex shape template, wherein theverification of the occurrence of the seizure is based upon both thedetermination that the heart beat complex shape fails to match thereference heart beat complex shape template and a second determinationthat the heart beat complex shape fails to match the second referenceheart beat complex shape template.
 13. The method of claim 1, whereinthe method further comprises taking an action in response to theverification, wherein the action is at least one of: providing a warningof the seizure; logging a time of the seizure; computing one or moreseizure indices; logging one or more computed seizure indices; providingat least one treatment of the seizure; and two or more thereof.
 14. Themethod of claim 1, wherein the obtaining further comprises obtainingdata relating to at least a portion of a plurality of heart beat complexshapes and the verification is based upon a determination that at leastone heart beat complex shape of the plurality of heart beat complexshapes fails to match the reference heart beat complex shape template.15. A method for indicating an occurrence of an epileptic seizure,comprising: obtaining via one or more processors of a medical device atleast one of cardiac data or kinetic data from a patient; indicating viathe one or more processors of the medical device a possible occurrenceof the epileptic seizure based at least in part upon the at least one ofthe cardiac data or the kinetic data; obtaining via the one or moreprocessors of the medical device a time series of heart beat complexdata from the patient; determining via the one or more processors of themedical device at least one heart beat complex shape parameter for eachof a plurality of heart beat complexes in the time series of heart beatcomplex data; comparing via the one or more processors of the medicaldevice the at least one heart beat complex shape parameter for each ofthe plurality of heart beat complexes to a first reference heart beatcomplex shape template; confirming via the one or more processors of themedical device the possible occurrence of the epileptic seizure as theoccurrence of the epileptic seizure based upon a determination that theat least one heart beat complex shape parameter for at least a portionof the plurality of heart beat complexes fails to match the firstreference heart beat complex shape template; providing a firstelectrical signal to the first cranial nerve structure of the patientusing a first polarity configuration in which the first electrodefunctions as a cathode and the second electrode functions as an anode,the first electrical signal is configured to induce action potentials inthe first cranial nerve structure, wherein a charge accumulates at theanode and the cathode as a result of the first electrical signal;switching from the first polarity configuration to a second polarityconfiguration upon termination of the first electrical signal where thefirst electrode functions as the anode and the second electrodefunctions as the cathode in the second polarity configuration; andproviding a second electrical signal to the second cranial nervestructure in the second polarity configuration, the second electricalsignal is configured to induce action potentials in the second cranialnerve structure where at least a portion of the second electrical signalcomprises the accumulated charge from the first electrical signal. 16.The method of claim 15, further comprising: in response to theconfirmation of the occurrence of the epileptic seizure, performing atleast one further action selected from: providing a warning; logging atleast one of an indication of the occurrence of the epileptic seizure,the confirmation of the occurrence of the epileptic seizure, a time ofthe confirmation of the occurrence of the epileptic seizure, and aseizure severity metric; and initiating at least one therapy to treatthe epileptic seizure.
 17. The method of claim 16, wherein the at leastone therapy is selected from: applying an electrical signal to a neuralstructure of the patient, wherein the neural structure is selected froma portion of a brain structure of the patient, a portion of a cranialnerve of the patient, a portion of a spinal cord of the patient, aportion of a sympathetic nerve structure of the patient, a portion of aparasympathetic nerve structure of the patient, and a portion of aperipheral nerve of the patient; delivering a drug to the patient; andcooling the neural structure of the patient.
 18. The method of claim 15,wherein determining at least one heart beat complex shape parametercomprises determining a plurality of heart beat complex shape parametersdetermining a shape of each of the plurality of heart beat complexes inthe time series; and wherein the comparing comprises comparing theplurality of heart beat complex shape parameters for each of theplurality of complexes to a corresponding plurality of reference heartbeat complex shape parameters defining the first reference heart beatcomplex shape template.
 19. The method of claim 15, wherein the firstreference heart beat complex shape template is selected from one of anon-ictal heart beat complex template, an ictal heart beat complextemplate, and a post-ictal heart beat complex template.
 20. The methodof claim 15, wherein determining at least one heart beat complex shapeparameter comprises using ECG data to determine a heart beat complexshape for each of the plurality of heart beat complexes in the timeseries, and wherein the first reference heart beat complex shapetemplate comprises a reference non-ictal PQRST complex template.